Legolas's Family History

This essay follows my Tolkien Canon Policy. Anything that does not contradict the text(s) above it is considered canon. Lord of the Rings is the first tier; The Hobbit, The Silmarillion, and The Children of Húrin are the second tier (as all – in some way – were not fully complete like LotR; however they are all individual books in their own right); and all other works and notes are in the third tier.

It may stand out to you that I do not use quotes from The Hobbit in this essay. That is because this essay is about the bigger Middle-earth mythology, and The Hobbit was not written with the intention of being part of the bigger mythology, thus leading to numerous inconsistencies that cannot be reconciled.

So I was reading an essay that argued for Thranduil and Celeborn being related (here; the author is called Gwed). Some of the information was inaccurate, but it got me thinking, and looking at the texts again. The implications I found were fascinating. Lets take a journey through elven history, shall we? (Bold is my emphasis)

First, let's establish one thing: While we don't know Thranduil's birth date, we know he lived in Doriath before its fall.

Most of these dwelt in Lindon west of the Ered Luin; but before the building of the Barad-dûr many of the Sindar passed eastward, and some established realms in the forests far away, where their people were mostly Silvan Elves. Thranduil, king in the north of Greenwood the Great, was one of these. - Lord of the Rings, Appendix B  

Others of the Eldar there were who crossed the mountains of Ered Luin in that age and passed into the inner lands. Many of these were Teleri, survivors of Doriath and Ossiriand; and they established realms among the Silvan Elves in woods and mountains far from the sea, for which nonetheless they ever yearned in their hearts. - The Silmarillion, Of the Rings of Power and the Third Age  

Remnants of the Telerian Elves (of Doriath in ancient Beleriand) establish realms in the woodlands far eastward, but most of these peoples are Avari or East-elves. The chief of these were Thranduil who ruled in the north of Greenwood the Great beyond Anduin, but Lórien was fairer and had the greater power; - The Peoples of Middle-earth, The Tales of Years of the Second Age, 750, T4  

This they did deliberately; for they (and other similar adventurers forgotten in the legends or only briefly named) came from Doriath after its ruin and had no desire to leave Middle-earth, nor to be merged with the other Sindar of Beleriand, dominated by the Noldorin Exiles for whom the folk of Doriath had no great love. - Unfinished Tales, The History of Galadriel and Celeborn, Appendix B

Remnants means “a small surviving group of people.” A small group of survivors from Doriath establish realms. The second two quotes explicitly state that Thranduil lived in Doriath. Only UT mentions Oropher, Thranduil's father; LotR App B says that Thranduil lead. As it is speaking in or after the Third Age (it's not until then that Thranduil is king), it's understandable why Oropher wasn't mentioned. However, Thranduil must have been old enough to help his father by co-leading; otherwise the text would have been worded differently.

We have proof that the text from LotR App B is simplified. In the Lóthlorien chapter, Legolas says, “It is long since any of my own folk journeyed hither back to the land whence we wandered in ages long ago,” and “The people of the woods did not delve in the ground like Dwarves, nor build strong places of stone before the Shadow came.” These lines prove that it is not as simple as LotR App B says.

It is noteworthy that Tolkien never considered any other history for Thranduil – his drafts all say that Thranduil was a Sindar from Doriath. There is no alternative.

“Similar adventurers” includes Amdír and Amroth, in Lórien.

So, we know that Celeborn, Oropher, Thranduil, Amdír, and Amroth lived in Doriath before its fall. Let's continue.

The people of Lórien were even then [i.e. at the time of the loss of Amroth] much as they were at the end of the Third Age: Silvan Elves in origin, but ruled by princes of Sindarin descent (as was the realm of Thranduil in the northern parts of Mirkwood; though whether Thranduil and Amroth were akin is not now known.)15 

15 See Appendix B, p.270, on the Sindarin princes of the Silvan Elves. - Unfinished Tales, The History of Galadriel and Celeborn, Amroth and Nimrodel

Wait! Sindarin princes? Thranduil and Amroth are family?

It says that it is no longer known if Thranduil and Amroth were related – thus implying that there is a relation. And princes? Regardless of how Tolkien uses the word 'prince' for men; when it comes to the elves, he uses it the way we would.

Which leads us to this:

[cut]; and their son Dior Eluchíl had to wife Nimloth, kinswoman of Celeborn, prince of Doriath, who was wedded to the Lady Galadriel. - The Silmarillion, The Ruin of Doriath

Celeborn, a prince of Doriath. How?

Galadriel, coming to Middle-earth as one of the leaders of the second host of the Noldor, met Celeborn in Doriath, and was later wedded to him; he was the grandson of Thingol's brother Elmo - a shadowy figure about whom nothing is told save that he was the younger brother of Elwë (Thingol) and Olwë, and was “beloved of Elwë with whom he remained.” (Elmo's son was named Galadhon, and his sons were Celeborn and Galathil; Galathil was the father of Nimloth, who wedded Dior Thingol's Heir and was the mother of Elwing. [cut]) - Unfinished Tales, The History of Galadriel and Celeborn

This text is not a full family tree, but an explanation of how Celeborn is related to Thingol and Nimloth. Also, there is something special about the names of Celeborn's family, something CT acknowledges:

The name Celeborn when first devised was intended to mean “Silver Tree”; it was the name of the Tree of Tol Eressëa (The Silmarillion p.59). Celeborn's close kin had “tree-names” (p.244): Galadhon his father, Galathil his brother, and Nimloth his niece, who bore the same name as the White Tree of Númenor. - Unfinished Tales, The History of Galadriel and Celeborn, Appendix E

Celeborn's close kin had tree-names. Oropher probably means “tall beech-tree,” and Amdír could mean “adult elm-tree” (if you go with Gwed's linguistic work, I'm not good enough at languages to be able to tell).

If the translations are true, that's two more tree-names. We know Thranduil means “vigorous spring,” and Amroth is said to have been a Silvan influenced nickname:

In another etymological discussion of the same period the name Amroth is explained as being a nickname derived from his living in a high talan or flet, the wooden platforms built high up in the trees of Lothlórien in which the Galadhrim dwelt (see The Fellowship of the Ring II 6): it meant “upclimber, high climber.” 16 - Unfinished Tales, Part 2: The Second Age, 4: The History of Galadriel and Celeborn, Amroth and Nimrodel 

Living in such lofty houses was no doubt at first thought remarkable, and Amroth was probably the first to do so. It was thus from his living in a high talan that his name - the only one that was later remembered in legend - was most probably derived. - Unfinished Tales, The History of Galadriel and Celeborn, Amroth and Nimrodel 

Certainly some names preserved from its past, such as Amroth and Nimrodel, cannot be fully explained from Sindarin, though fitting it in form. - Unfinished Tales, The History of Galadriel and Celeborn, Appendix A 

But Lórien, Caras Galadhon, Amroth, Nimrodel are probably of Silvan origin, adapted to Sindarin. - Lord of the Rings, Appendix F

Regardless of names, it cannot be denied that Celeborn, Oropher, Thranduil, Amdír, and Amroth are all Sindarin princes. That is stated explicitly.

It is also stated explicitly that the only Sindarin royalty still alive was Thingol's family:

But the victory of the Elves was dear-bought. For those of Ossiriand were light-armed, and no match for the Orcs, who were shod with iron and iron-shielded and bore great spears with broad blades; and Denethor was cut off and surrounded upon the hill of Amon Ereb. There he fell and all his nearest kin about him, before the host of Thingol could come to his aid. Bitterly though his fall was avenged, when Thingol came upon the rear of the Orcs and slew them in heaps, his people lamented him ever after and took no king again. - The Silmarillion, Of the Sindar

Finally, Celeborn himself gives us the most evidence:

Celeborn: “Welcome son of Thranduil! Too seldom do my kindred journey hither from the North.” - Lord of the Rings, Mirror of Galadriel

When greeting Legolas, Celeborn refers to Thranduil and says “my kindred”. It is crucial to note that he says “my” and not “our”; and it doesn't make sense if we translate this as just a reference to being Sindarin – there are many other Sindar in Lothlórien:

In Lórien, where many of the people were Sindar in origin, or Noldor, survivors from Eregion [see p. 255], Sindarin had become the language of all the people. - Unfinished Tales, Part 2: The Second Age, 4: The History of Galadriel and Celeborn, Appendix A

Celeborn is clearly saying that they are his kin specifically.

Incidentally, the question of Elven hair colors also gives us some very interesting information.

The Elves far back in the Elder Days became divided into two main branches: the West-elves (the Eldar) and the East-elves. 

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The Grey-elven was in origin akin to Quenya; for it was the language of those Eldar who, coming to the shores of Middle-earth, had not passed over the Sea but had lingered on the coasts in the country of Beleriand. 

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Elves has been used to translate both Quendi, 'the speakers', the High-elven name for all their kind, and Eldar, the name of the Three Kindreds that sought for the Undying Realm and came there at the beginning of Days (save the Sindar only). [cut] They were a race high and beautiful, the older Children of the world, and among them the Eldar were as kings, who now are gone: the People of the Great Journey, the People of the Stars. They were tall, fair of skin and grey- eyed, though their locks were dark, save in the golden house of Finarfin; and their voices had more melodies than any mortal voice that now is heard. They were valiant, but the history of those that returned to Middle-earth in exile was grievous; and though it was in far-off days crossed by the fate of the Fathers, their fate is not that of Men. Their dominion passed long ago, and they dwell now beyond the circles of the world, and do not return. - Lord of the Rings, Appendix F

Since this is from the in-universe translator of LotR, it is best understood as a summary of the Noldor and Sindar pulled from texts most familiar with the Noldor (after all, the Vanyar never returned to Middle-earth, and so have no bearing on LotR).

Vanyar. This name was probably given to the First Clan by the Noldor. They accepted it, but continued to call themselves most often by their old numerical name Minyar (since the whole of this clan had joined the Eldar and reached Aman). The name referred to the hair of the Minyar, which was in nearly all members of the clan yellow or deep golden. This was regarded as a beautiful feature by the Noldor (who loved gold), though they were themselves mostly dark- haired. Owing to intermarriage the golden hair of the Vanyar sometimes later appeared among the Noldor: notably in the case of Finarfin, and in his children Finrod and Galadriel, in whom it came from King Finwë's second wife, Indis of the Vanyar. 

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Elwë himself had indeed long and beautiful hair of silver hue, but this does not seem to have been a common feature of the Sindar, though it was found among them occasionally, especially in the nearer or remoter kin of Elwë (as in the case of Círdan).(15) In general the Sindar appear to have very closely resembled the Exiles, being dark-haired, strong and tall, but lithe. Indeed they could hardly be told apart except by their eyes; for the eyes of all the Elves that had dwelt in Aman impressed those of Middle-earth by their piercing brightness. - The War of the Jewels, Quendi and Eldar

This matches what LotR App F tells us. The majority of both the Noldor and the Sindar were dark-haired, with a few exceptions. After all, Glorfindel is another example of golden hair among the Noldor.

But our focus is on the Sindar. This text mentioned that Círdan has silver hair because he is a distant kinsman of Thingol.

On two chairs beneath the bole of the tree and canopied by a living bough there sat, side by side, Celeborn and Galadriel. They stood up to greet their guests, after the manner of Elves, even those who were accounted mighty kings. Very tall they were, and the Lady no less tall than the Lord; and they were grave and beautiful. They were clad wholly in white; and the hair of the Lady was of deep gold, and the hair of the Lord Celeborn was of silver long and bright; but no sign of age was upon them, unless it were in the depths of their eyes; for these were keen as lances in the starlight, and yet profound, the wells of deep memory. - Lord of the Rings, The Mirror of Galadriel 

[Finarfin] wedded Eärwen, the daughter of King Olwë of Alqualondë, and his children were thus the kin of King Elu Thingol of Doriath in Beleriand, for he was the brother of Olwë; and this kinship influenced their decision to join in the Exile, and proved of great importance later in Beleriand. 

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Even among the Eldar [Galadriel] was accounted beautiful, and her hair was held a marvel unmatched. It was golden like the hair of her father and of her foremother Indis, but richer and more radiant, for its gold was touched by some memory of the starlike silver of her mother; and the Eldar said that the light of the Two Trees, Laurelin and Telperion, had been snared in her tresses. - Unfinished Tales, The History of Galadriel and Celeborn

Celeborn's hair is completely silver, and Galadriel's is “touched by some memory” of Thingol's and his family's characteristic silver hair.

Now, here's where things get really interesting. In The Hobbit, Flies and Spiders, Thranduil is described as “a woodland king with a crown of leaves on his golden hair.”

Now, I don't usually quote from The Hobbit because it was not written with the intention of being part of the bigger mythology, and there are numerous inconsistencies that cannot be reconciled between it and the mythology. However, Thranduil having golden hair actually fits.

Because Amroth also has golden hair:

The mariners with their Elvish sight for a long time could see him battling with the waves, until the rising sun gleamed through the clouds and far off lit his bright hair like a spark of gold. - Unfinished Tales, The History of Galadriel and Celeborn, Amroth and Nimrodel

So both Thranduil and Amroth are said to be Sindarin princes, and they both have golden hair. How? We are not told. But it must have come from a Vanyar ancestor. Combining all of the clues we have been given, I theorize that Thingol has another sibling; one who married a Vanyar. Oropher and Amdír would be their sons, and Thranduil and Amroth would be their grandsons.

Is there any explicit evidence for this? No. But it fits perfectly with all the facts we are given. We cannot forget that it is explicitly stated that Thranduil and Celeborn are kin, and that Thranduil was a Sindarin prince.

We are now moving on to the Second Age. This is what I said in my Tauriel essay, to summarize the First Age:

Thranduil would have survived the first sack of Doriath (done by dwarves), and the second sack (which was also the second kinslaying between elves). Thranduil and his father, being two of the few who survived, fled to the secret haven in the mouths of Sirion. However there was once again a massacre, when the sons of Fëanor did their third kinslaying. The few who survived that (Oropher and Thranduil included) fled to the isle of Balar, which became a refugee camp. They stayed there while the host of Valinor defeated Morgoth, and then briefly lived in Lindon, before traveling to the Greenwood.

Now we look at what Unfinished Tales, The History of Galadriel and Celeborn, Appendix B says. First, it must be assumed that Elmo, Galadhon, and Galathil are dead by the beginning of the Second Age; as they are never mentioned again.

Oropher had come among them with only a handful of Sindar, and they were soon merged with the Silvan Elves, adopting their language and taking names of Silvan form and style. This they did deliberately; for they (and other similar adventurers forgotten in the legends or only briefly named) came from Doriath after its ruin and had no desire to leave Middle-earth, nor to be merged with the other Sindar of Beleriand, dominated by the Noldorin Exiles for whom the folk of Doriath had no great love. They wished indeed to become Silvan folk and to return, as they said, to the simple life natural to the Elves before the invitation of the Valar had disturbed it.

It must be noted quickly that what Tolkien wrote here, in regards to language, is contradicted by his other writings on the matter. The Silvan elves adopted Sindarin:

Of the latter kind were most of the Elven-folk of Mirkwood and Lórien; but their languages do not appear in this history, in which all the Elvish names and words are of Eldarin form.1 

1 In Lórien at this period Sindarin was spoken, though with an 'accent', since most of its folk were of Silvan origin. This 'accent' and his own limited acquaintance with Sindarin misled Frodo (as is pointed out in The Thain's Book by a commentator of Gondor). All the Elvish words cited in Book Two chs 6, 7, 8 are in fact Sindarin, and so are most of the names of places and persons. - Lord of the Rings, Appendix F

This is specifically talking about Lórien because that is where the Fellowship travels to, however, it is still relevant when discussing the Woodland Realm.

Tolkien also says, in Unfinished Tales, The History of Galadriel and Celeborn, Appendix A:

The Silvan Elves hid themselves in woodland fastnesses beyond the Misty Mountains, and became small and scattered people, hardly to be distinguished from Avari; but they still remembered that they were in origin Eldar, members of the Third Clan, and they welcomed those of the Noldor and especially the Sindar who did not pass over the Sea but migrated eastward [i.e. at the beginning of the Second Age]. Under the leadership of these they became again ordered folk and increased in wisdom. Thranduil father of Legolas of the Nine Walkers was Sindarin, and that tongue was used in his house, though not by all his folk. 

In Lórien, where many of the people were Sindar in origin, or Noldor, survivors from Eregion [see p. 255], Sindarin had become the language of all the people. In what way their Sindarin differed from the forms of Beleriand – see The Fellowship of the Ring II 6, where Frodo reports that the speech of the Silvan folk that they used among themselves was unlike that of the West - is now of course not known. It probably differed in little more than what would now popularly called "accent": mainly differences of vowel-sounds and intonation sufficient to mislead one who, as Frodo, was not well acquainted with purer Sindarin. There may of course also have been some local words and other features ultimately due to the influence of the former Silvan tongue. Lórien had long been much isolated from the outside world. Certainly some names preserved from its past, such as Amroth and Nimrodel, cannot be fully explained from Sindarin, though fitting it in form. Caras seems to be an old word for a moated fortress, not found in Sindarin. Lórien is probably an alteration of an older name now lost [though earlier the original Silvan or Nandorin name was stated to be Lórinand, see p.265, note 5]. 

and: 

Though the comparison of the Silvan dialects with their own speech greatly interested the loremasters, especially those of Noldorin origin, little is now known of the Silvan Elvish. The Silvan Elves had invented no forms of writing, and those who learned this art from the Sindar wrote in Sindarin as well as they could. By the end of the Third Age the Silvan tongues had probably ceased to be spoken in the two regions that had importance at the time of the War of the Ring: Lórien and the realm of Thranduil in northern Mirkwood. All that survived of them in the records was a few words and several names of persons and places.

So here are two more texts on the matter. The first one says that most but not all of the Woodland Elves spoke Sindarin. The second one says that by the end of the Third Age all spoke (and wrote) Sindarin. The one above (from UT App B) says that Oropher and the Sindarin elves adopted the Silvan language and took Silvan names.

Which one of these three is true? We can rule out the one from UT App B immediately, because both Oropher and Thranduil are completely Sindarin names. The two names of the Woodland Realm, Eryn Galen and Eryn Lasgalen, are also completely Sindarin. As I will go over in a little bit, Legolas's name is literally the only case we have where a Sindarin word is Silvanized.

So, what about UT App A? The first text implies that the Silvan tongue was still spoken at the end of the Third Age, however it also implies that the number of Elves using the Silvan tongue was minimal. It explicitly states that Thranduil and most of his people spoke Sindarin (if it was not most, then the text should read “though not by most of his folk”).

Also, we cannot forget that all of the Woodland Elves seem to be fluent in Westron, and that they have much more contact with other kingdoms and peoples than Lothlórien (mainly Dale and Erebor, but also Dorwinion). Dorwinion itself is Sindarin, and Tolkien said: “was probably far south down the R. Running, and its Sindarin name a testimony to the spread of Sindarin: in this case expectable since the cultivation of vines was not known originally to the Nandor or Avari.”

Combining everything, I find it very hard to believe the Silvan tongue was still frequently used by the end of the Third Age. It just doesn't make any sense.

None of this changes the motives and opinions of the characters, however. The text shows a clear divide between Oropher and Celeborn. Oropher blames the dwarves, the Noldor, and the Valar for the devastation that was wrought during the First Age. This is not a new viewpoint, as Thingol had the same opinion of the Noldor:

Now King Thingol welcomed not with a full heart the coming of so many princes in might out of the West, eager for new realms; and he would not open his kingdom, nor remove its girdle of enchantment, for wise with the wisdom of Melian he trusted not that the restraint of Morgoth would endure. Alone of the princes of the Noldor those of Finarfin's house were suffered to pass within the confines of Doriath; for they could claim close kinship with King Thingol himself, since their mother was Eärwen of Alqualondë, Olwë's daughter. - The Silmarillion, Of the Return of the Noldor 

But Thingol was long silent ere he spoke. “Go now!” he said. “For my heart is hot within me. Later you may return, if you will; for I will not shut my doors for ever against you, my kindred, that were ensnared in an evil that you did not aid. With Fingolfin and his people also I will keep friendship, for they have bitterly atoned for such ill as they did. And in our hatred of the Power that wrought all this woe our griefs shall be lost. But hear my words! Never again in my ears shall be heard the tongue of those who slew my kin in Alqualondë! Nor in all my realm shall it be openly spoken, while my power endures. All the Sindar shall hear my command that they shall neither speak with the tongue of the Noldor nor answer to it. And all such as use it shall be held slayers of kin and betrayers of kin unrepentant.” 

Then the sons of Finarfin departed from Menegroth with heavy hearts, perceiving how the words of Mandos would ever be made true, and that none of the Noldor that followed after Fëanor could escape from the shadow that lay upon his house. And it came to pass even as Thingol had spoken; for the Sindar heard his word, and thereafter throughout Beleriand they refused the tongue of the Noldor, and shunned those that spoke it aloud; but the Exiles took the Sindarin tongue in all their daily uses, and the High Speech of the West was spoken only by the lords of the Noldor among themselves. - The Silmarillion, Of the Noldor in Beleriand

Celeborn had the opposite opinion; being both Galadriel's husband, and becoming a lord of the other Sindar under Gil-Galad:

In Lindon south of the Lune dwelt for a time Celeborn, kinsman of Thingol; his wife was Galadriel, greatest of Elven women. - Lord of the Rings, Appendix B 

In a note in unpublished material the Elves of Harlindon, or Lindon south of the Lune, are said to have been largely of Sindarin origin, and the region to have been a fief under the rule of Celeborn. - Unfinished Tales, The History of Galadriel and Celeborn, Note 2 

Gil-galad's people were mainly Noldorin; though in the Second Age the Elves of Harlindon were mainly Sindarin, and the region was a fief under the rule of Celeborn. - The Peoples of Middle-earth, Of Dwarves and Men

The text implies that Amdír agreed with Oropher, and that was why he traveled east (again, “other similar adventurers” can only refer to Lórien).

However, the next passage shows a curious contradiction:

In the Second Age their king, Oropher [the father of Thranduil, father of Legolas], had withdrawn northward beyond the Gladden Fields. This he did to be free from the power and encroachments of the Dwarves of Moria, which had grown to be the greatest of the mansions of the Dwarves recorded in history; and also he resented the intrusions of Celeborn and Galadriel into Lórien. - Unfinished Tales, The History of Galadriel and Celeborn, Appendix B

Encroachment means “to intrude gradually, stealthily, or insidiously upon the rights, property, etc, of another.” Resentment means “indignation or ill will stemming from a feeling of having been wronged or offended.” Intrusion means “an inappropriate or unwelcome addition.”

Oropher felt that the dwarves were getting too powerful, and intruding where they didn't belong. There was possible conflict between the elves and dwarves at this time (for more on this, and the relationships between elves and dwarves, see here). Feeling wronged, he had a large amount of ill will for noldo Galadriel and her turncoat husband. That is clear.

It is also clear that while Amdír didn't want to live in a land dominated by the Noldor, he didn't have a problem with Galadriel and Celeborn:

They had however been much mingled with Noldor (of Sindarin speech), who passed through Moria after the destruction of Eregion by Sauron in the year 1697 of the Second Age. At that time Elrond went westward [sic; probably meaning simply that he did not cross Misty Mountains] and established the refuse of Imladris; Celeborn went at first to Lórien and fortified it against any further attempts of Sauron to cross the Anduin. When however Sauron withdrew to Mordor, and was (as reported) wholly concerned with conquests in the East, Celeborn rejoined Galadriel in Lindon. 

Lórien had then long years of peace and obscurity under the rule of its own king Amdír, until the Downfall of Númenor and the sudden return of Sauron to Middle-earth. 

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The implication of the extract just given is that after Eregion's fall Celeborn led this migration to Lórien, while Galadriel joined Gil-galad in Lindon; but elsewhere, in a writing contemporary with this, it is said explicitly that they both at that time “passed through Moria with a considerable following of Noldorin exiles and dwelt for many years in Lórien.” 

And: 

To Lórien Celeborn and Galadriel returned twice before the Last Alliance and the end of the Second Age;[cut]. - (All from Unfinished Tales, The History of Galadriel and Celeborn, Amroth and Nimrodel)

From this, it appears that Galadriel and Celeborn moved to Eregion at some point, and began to have an ongoing relationship with Lórien.

We will never know, but I wonder what caused Oropher to essentially reject all kinship to Celeborn, when Amdír didn't?

Also, while Oropher wanted nothing to do with Lórien, he did not force his viewpoint on his subjects:

But as yet there was little to fear between the Greenwood and the Mountains and there was constant intercourse between his people and their kin across the river, until the War of the Last Alliance. - Unfinished Tales, The History of Galadriel and Celeborn, Appendix B

This matches with what Legolas says in Lord of the Rings, Lóthlorien: “It is long since any of my own folk journeyed hither back to the land whence we wandered in ages long ago.”

There is another text that needs to be mentioned. Tolkien wrote another account of Oropher in Unfinished Tales, The Disaster of the Gladden Fields, Note 14. He says:

Three times he had moved northwards, and at the end of the Second Age he dwelt in the western glens of the Emyn Duir, and his numerous people lived and roamed in the woods and vales westward as far as Anduin, north of the ancient Dwarf-Road (Men-i-Naugrim).

This contradicts the text I have been using. It also doesn't make much sense.

According to this, Oropher moved northwards three times, and at least one of those three took place after the War of the Elves and Sauron (otherwise “at the end of the Second Age” would be “by the beginning of the war of Elves and Sauron”). The War of the Elves and Sauron took place in Eriador. Of Dwarves and Men also tells us:

The Second Age had reached only the middle of its course (c. Second Age 1695) when he invaded Eriador and destroyed Eregion, a small realm established by the Eldar migrating from the ruin of Beleriand that had formed an alliance also with the Longbeards of Moria. This marked the end of the Alliance of the Longbeards with Men of the North. For though Moria remained impregnable for many centuries, the Orks reinforced and commanded by servants of Sauron invaded the mountains again. Gundabad was re-taken, the Ered Mithrin infested and the communication between Moria and the Iron Hills for a time cut off. The Men of the Alliance were involved in war not only with Orks but with alien Men of evil sort. For Sauron had acquired dominion over many savage tribes in the East (of old corrupted by Morgoth), and he now urged them to seek land and booty in the West. When the storm passed,(35) the Men of the old Alliance were diminished and scattered, and those that lingered on in their old regions were impoverished, and lived mostly in caves or in the borders of the Forest. 

35. Sauron was defeated by the Numenoreans and driven back into Mordor, and for long troubled the West no more, while secretly extending his dominions eastward.

LotR App B tells us that all of this begins in SA 1693, and ends in SA 1701. No battle ever came to Lórien, or the Greenwood. As Amroth and Nimrodel said, they had “long years of peace and obscurity” afterwards.

So, it makes no sense that Oropher would keep moving them north, after war had devastated the lands around the northern end of the Greenwood, to essentially where they are in The Hobbit (if you look at a map, the western glens are almost at the Forest Gate/Elf-path); and that none of his people would journey to see their kin in Lórien, even though there was no danger or darkness in the forest or surrounding areas.

Therefore, this part of Note 14 must be discarded. However, this text does give us some more relevant information.

Note 12 says:

12 Amon Lanc, "Naked Hill," was the highest point in the highland at the south-west corner of the Greenwood, and was so called because no trees grew on its summit. In later days it was Dol Guldur, the first stronghold of Sauron after his awakening.

And Note 14 starts with:

14 Long before the War of the Alliance, Oropher, King of the Silvan Elves east of Anduin, being disturbed by rumours of the rising power of Sauron, had left their ancient dwellings about Amon Lanc, across the river from their kin in Lórien.

As we went over, Note 14 contradicts all of the other texts, so the reasoning given here cannot be accepted (fear of Sauron). However, Oropher must have had a capitol somewhere before he moved north, and Amon Lanc is the perfect geographical location – it is directly across from Lórien. This fits with the main text we have been using. It also makes for another fascinating twist – Sauron took Thranduil's former home and turned it into his fortress.

This brings us to the War of the Last Alliance.

Despite the desire of the Silvan Elves to meddle as little as might be in the affairs of the Noldor and Sindar, or of any other peoples, Dwarves, Men, or Orcs, Oropher had the wisdom to foresee that peace would not return unless Sauron was overcome. He therefore assembled a great army of his now numerous people, and joining with the lesser army of [Amdír] of Lórien he led the host of the Silvan Elves to battle. The Silvan Elves were hardy and valiant, but ill-equipped with armour or weapons in comparison with the Eldar of the West; also they were independent, and not disposed to place themselves under the supreme command of Gil-galad. Their losses were thus more grievous than they need have been, even in that terrible war. [Amdír] and more than half his following perished in the great battle of the Dagorlad, being cut off from the main host and driven into the Dead Marshes. Oropher was slain in the first assault upon Mordor, rushing forward at the head of his most doughty warriors before Gil-galad had given the signal for the advance. Thranduil his son survived, but when the war ended and Sauron was slain (as it seemed) he led back home barely a third of the army that had marched to war. - Unfinished Tales, The History of Galadriel and Celeborn, Appendix B

And: 

Amdír obeyed the summons of Gil-galad and brought as large a force as he could muster to the Last Alliance, but he was slain in the Battle of Dagorlad and most of his company with him. Amroth, his son, became king. - Unfinished Tales, The History of Galadriel and Celeborn, Amroth and Nimrodel

Lots to go over here. Oropher “had the wisdom to foresee” and “therefore assembled a great army”. Amdír “obeyed the summons of Gil-galad”. Amdír goes to war because he was summoned. Oropher goes to war because of his personal belief.

Both had their pride, and refused to put themselves entirely under Gil-galad's command. Though, like all else, their fates are distinctly different.

Oropher, in his pride, took Thranduil and his best warriors, and rashly charged the host of Mordor before the signal. Surely he couldn't have thought that they alone could take on all of Mordor?

Thranduil watched his father (and many of their people) be uselessly slaughtered for his father's pride, which made him become king at the very beginning of the war.

Amdír was smart, and waited for the signal. However, his army got separated from the main force. He and more than half of his people were killed in the Dead Marshes. Amroth became king.

Oropher and Amdír would have been two of the bodies in the Dead Marshes in LotR, tainted by Sauron's power:

He first saw one with the corner of his left eye, a wisp of pale sheen that faded away; but others appeared soon after: some like dimly shining smoke, some like misty flames flickering slowly above unseen candles; here and there they twisted like ghostly sheets unfurled by hidden hands. But neither of his companions spoke a word. 

At last Sam could bear it no longer. “What's all this, Gollum?” he said in a whisper. “These lights? They're all round us now. Are we trapped? Who are they?” 

Gollum looked up. A dark water was before him, and he was crawling on the ground, this way and that, doubtful of the way. “Yes, they are all round us,” he whispered. “The tricksy lights. Candles of corpses, yes, yes. Don't you heed them! Don't look! Don't follow them! Where's the master?” 

Sam looked back and found that Frodo had lagged again. He could not see him. He went some paces back into the darkness, not daring to move far, or to call in more than a hoarse whisper. Suddenly he stumbled against Frodo, who was standing lost in thought, looking at the pale lights. His hands hung stiff at his sides; water and slime were dripping from them. 

“Come, Mr. Frodo!” said Sam. “Don't look at them! Gollum says we mustn't. Let's keep up with him and get out of this cursed place as quick as we can - if we can!” 

“All right,” said Frodo, as if returning out of a dream. 'I'm coming. Go on!” 

Hurrying forward again, Sam tripped, catching his foot in some old root or tussock. He fell and came heavily on his hands, which sank deep into sticky ooze, so that his face was brought close to the surface of the dark mere. There was a faint hiss, a noisome smell went up, the lights flickered and danced and swirled. For a moment the water below him looked like some window, glazed with grimy glass, through which he was peering. Wrenching his hands out of the bog, he sprang back with a cry. “There are dead things, dead faces in the water,” he said with horror. “Dead faces!” 

Gollum laughed. “The Dead Marshes, yes, yes: that is their names,” he cackled. “You should not look in when the candles are lit.” 

“Who are they? What are they?” asked Sam shuddering, turning to Frodo, who was now behind him. 

“I don't know,” said Frodo in a dreamlike voice. “But I have seen them too. In the pools when the candles were lit. They lie in all the pools, pale faces, deep deep under the dark water. I saw them: grim faces and evil, and noble faces and sad. Many faces proud and fair, and weeds in their silver hair. But all foul, all rotting, all dead. A fell light is in them.” Frodo hid his eyes in his hands. “I know not who they are; but I thought I saw there Men and Elves, and Orcs beside them.” 

“Yes, yes,” said Gollum. “All dead, all rotten. Elves and Men and Orcs. The Dead Marshes. There was a great battle long ago, yes, so they told him when Sméagol was young, when I was young before the Precious came. It was a great battle. Tall Men with long swords, and terrible Elves, and Orcses shrieking. They fought on the plain for days and months at the Black Gates. But the Marshes have grown since then, swallowed up the graves; always creeping, creeping.” 

“But that is an age and more ago,” said Sam. “The Dead can't be really there! Is it some devilry hatched in the Dark Land?” 

“Who knows? Sméagol doesn't know,” answered Gollum. “You cannot reach them, you cannot touch them. We tried once, yes, precious. I tried once; but you cannot reach them. Only shapes to see, perhaps, not to touch. No precious! All dead.” - Lord of the Rings, The Passage of the Marshes

After seven years of war (see LotR App B), Thranduil led “barely a third” of his warriors home.

Thranduil his son had returned with the remnant of the army of the Silvan Elves in the year before Isildur's march. - Unfinished Tales, The Disaster of the Gladden Fields, Note 14 

In the event the main might of Gil-galad, together with Isildur and part of the Men of Arnor, had come over the Passes of Imladris and Caradhras, and the Orcs were dismayed and hid themselves. But they remained alert and watchful, determined to attack any companies of Elves or Men that they outnumbered. Thranduil they had let pass, for even his diminished army was far too strong for them; but they bided their time, for the most part hidden in the Forest, while others lurked along the riverbanks. It is unlikely that any news of Sauron's fall had reached them, for he had been straitly besieged in Mordor and all his forces had been destroyed. If any few had escaped, they had fled far to the East with the Ringwraiths. This small detachment in the North, of no account, was forgotten. Probably they thought that Sauron had been victorious, and the war-scarred army of Thranduil was retreating to hide in fastnesses of the Forest. - Unfinished Tales, The Disaster of the Gladden Fields, Note 20

Thranduil and his army were left unhindered on their way home.

The Second Age has ended, we are now on to the Third Age.

A long peace followed in which the numbers of the Silvan Elves grew again; but they were unquiet and anxious, feeling the change of the world that the Third Age would bring. Men also were increasing in numbers and in power. The dominion of the Númenórean kings of Gondor was reaching out northwards towards the borders of Lórien and the Greenwood. The Free Men of the North (so called by the Elves because they were not under the rule of Dúnedain, and had not for the most part been subjected by Sauron or his servants) were spreading southwards: mostly east of the Greenwood, though some were establishing themselves in the eaves of the forest and the grasslands of the Vales of Anduin. More ominous were rumours from the further East: the Wild Men were restless. Former servants and worshippers of Sauron, they were released now from his tyranny, but not from the evil and darkness that he had set in their hearts. Cruel wars raged among them, from which some were withdrawing westward, with minds filled with hatred, regarding all that dwelt in the West as enemies to be slain and plundered. But there was in Thranduil's heart a still deeper shadow. He had seen the horror of Mordor and could not forget it. If ever he looked south its memory dimmed the light of the Sun, and though he knew that it was now broken and deserted and under the vigilance of the Kings of Men, fear spoke in his heart that it was not conquered for ever: it would arise again. - Unfinished Tales, The History of Galadriel and Celeborn, Appendix B

Remember, one of the quotes above states that the Silvan elves had no contact with their kin in Lórien, after the Last Alliance.

Thranduil returns from the war not only as King, but also deeply traumatized. This is very, very important.

In my Tauriel essay, I summarized elvish nature:

The foundation of elven-kind is memory and emotion. Their mind/will/soul controls their body, because their souls are bound to the Unseen Plane. This means so many things. They feel bodily desires, but the desires have no control or sway over them. Let me give an example. If we touch a hot surface our body responds immediately, jerking back. Our body is in control, we don't consciously decide to move back. That's not true for elves. Their body never overrides their mind.

Elvish memories remain crystal clear, no matter how many decades or centuries pass. They never fade, even the slightest bit. Connected to memory is emotion. Elves feel things in a clearer way. They are ruled by emotion. They can literally just lie down and kill themselves with their mind, if they wish.

Thranduil's memories of the first two ages will never dim. His trauma will never fade. He knows Sauron is not defeated, and he is terrified of Sauron returning.

When maybe a thousand years had passed, and the first shadow had fallen on Greenwood the Great, the Istari or Wizards appeared in Middle-earth. 

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TA 1050: About this time a shadow falls on Greenwood, and men begin to call it Mirkwood. - Lord of the Rings, Appendix B 

When a thousand years of the Third Age had passed and the Shadow fell upon Greenwood the Great, the Silvan Elves ruled by Thranduil retreated before it as it spread ever northward, until at last Thranduil established his realm in the north-east of the forest and delved there a fortress and great halls underground. Oropher was of Sindarin origin, and no doubt Thranduil his son was following the example of King Thingol long before, in Doriath; though his halls were not to be compared with Menegroth. He had not the arts nor wealth nor the aid of the Dwarves; and compared with the Elves of Doriath his Silvan folk were rude and rustic. - Unfinished Tales, The History of Galadriel and Celeborn, Appendix B

Note 14 is again contradicted here. The phrases “retreated before it”, “spread ever northward”, and “until at last” denote a large amount of time passes, and that Thranduil makes many moves northward (these moves start around TA 1050). That is simply not possible if Oropher had already moved them north of the mountains.

One of Gimli's lines is also contradicted here: “Do you think those halls are fair, where your King dwells under the hill in Mirkwood, and Dwarves helped in their making long ago?” - Lord of the Rings, The Road to Isengard

As LotR takes precedence, we know that Thranduil had the help of dwarves (probably from the Grey Mountains) to build his palace, which he did in remembrance of Menegroth (this is another mention of Thranduil's connection to Doriath). He fears Sauron, and wants an impenetrable fortress.

This also matches with what Legolas says in Lord of the Rings, Lóthlorien: “The people of the woods did not delve in the ground like Dwarves, nor build strong places of stone before the Shadow came.”

When did this happen?

c. TA 1100: The Wise (the Istari and the chief Eldar) discover that an evil power has made a stronghold at Dol Guldur. It is thought to be one of the Nazgûl. 

c. TA 1300: Evil things begin to multiply again. Orcs increase in the Misty Mountains and attack the Dwarves. The Nazgûl reappear. The chief of these comes north to Angmar. 

TA 1981: The dwarves flee from Moria. Many of the Silvan Elves of Lórien flee south. Amroth and Nimrodel are lost. 

TA 1999: Thráin I comes to Erebor and founds a dwarf-kingdom 'under the Mountain'. - Lord of the Rings, Appendix B 

[Thranduil's realm] extended into the woods surrounding the Lonely Mountain and growing along the west shores of the Long Lake, before the coming of the Dwarves exiled from Moria and the invasion of the Dragon. The Elvish folk of this realm had migrated from the south, being the kin and neighbours of the Elves of Lórien; but they had dwelt in Greenwood the Great east of Anduin.

This is the last quote from UT, App B. It tells us that Thranduil's realm was already in the north-east by TA 1999. Can we narrow down that 1000 years any further? Judging by LotR App B, it was probably early on.

But the Dominion of Men was preparing and all things were changing, until at last the Dark Lord arose in Mirkwood again. 

Now of old the name of that forest was Greenwood the Great, and its wide halls and aisles were the haunt of many beasts and of birds of bright song; and there was the realm of King Thranduil under the oak and the beech. But after many years, when well nigh a third of that age of the world had passed, a darkness crept slowly through the wood from the southward, and fear walked there in shadowy glades; fell beasts came hunting, and cruel and evil creatures laid there their snares. 

Then the name of the forest was changed and Mirkwood it was called, for the nightshade lay deep there, and few dared to pass through, save only in the north where Thranduil’s people still held the evil at bay. Whence it came few could tell, and it was long ere even the Wise could discover it. It was the Shadow of Sauron and the sign of his return. For coming out of the wastes of the East he took up his abode in the south of the forest, and slowly he grew and took shape there again; in a dark hill he made his dwelling and wrought there his sorcery, and all folk feared the Sorcerer of Dol Guldur, and yet they knew not at first how great was their peril. 

Even as the first shadows were felt in Mirkwood there appeared in the west of Middle-earth the Istari, whom Men called the Wizards. - The Silmarillion, Of the Rings of Power and the Third Age

This summarizes Sauron's return, and tells us the effects of his presence in the Greenwood.

Around TA 1300 would be the most likely time – the 250 years gives Thranduil time to move gradually, but is still early on in Sauron's return. His terror is at the forefront here – the general consensus may be that it was one of the Nazgûl; but Thranduil's trauma and fear would always be whispering in the back of this mind, tormenting him with the possibility of it being Sauron.

His state of mind would not have been helped by Galadriel and Celeborn's behavior, either.

Amroth was King of Lórien, after his father Amdír was slain in the Battle of Dagorlad [in the year 3434 of the Second Age]. His land had peace for many years after the defeat of Sauron. Though Sindarin in descent he lived after the manner of the Silvan Elves and housed in the tall trees of a great green mound, ever after called Cerin Amroth. This he did because of his love for Nimrodel. 

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But during the Third Age Galadriel became filled with foreboding, and with Celeborn she journeyed to Lórien and stayed there long with Amroth, being especially concerned to learn all news and rumours of the growing shadow in Mirkwood and the dark stronghold in Dol Guldur. But his people were content with Amroth; he was valiant and wise, and his little kingdom was yet prosperous and beautiful. Therefore after long journeys of enquiry in Rhovanion, from Gondor and the borders of Mordor to Thranduil in the north, Celeborn and Galadriel passed over the mountains to Imladris, and there dwelt for many years; for Elrond was their kinsman, since he had early in the Third Age [in the year 109, according to the Tale of Years] wedded their daughter Celebrían. 

After the disaster in Moria [in the year 1980] and the sorrows of Lórien, which was now left without a ruler (for Amroth was drowned in the sea in the Bay of Belfalas and left no heir), Celeborn and Galadriel returned to Lórien, and were welcomed by the people. There they dwelt while the Third Age lasted, but they took no title of King or Queen; for they said that they were only guardians of this small but fair realm, the last eastward outpost of the Elves. 

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[cut]; and in the Third Age, when the shadow of Sauron's recovery arose, they dwelt there again for a long time. - Unfinished Tales, The History of Galadriel and Celeborn, Amroth and Nimrodel

Lórien had peace, unlike the Greenwood. Around TA 1100, Galadriel and Celeborn moved there, worried about the Shadow. A few centuries later, they journeyed across Middle-earth, trying to gather information.

It is notable that they visit Thranduil. Their visit must have increased the terror in him, about the Shadow.

Galadriel and Celeborn spend the remainder of the years before TA 1981 in Rivendell. The “last eastward outpost of the Elves,” line makes no sense, as Thranduil and the Woodland Realm are further east. Nor would Galadriel and Celeborn say that, because Thranduil is kin. The line is a mistake on Tolkien's part.

TA 2060: The power of Dol Guldur grows. The Wise fear that it may be Sauron taking shape again. 

TA 2063: Gandalf goes to Dol Guldur. Sauron retreats and hides in the East. The Watchful Peace begins. - Lord of the Rings, Appendix B 

Ever most vigilant was Mithrandir, and he it was that most doubted the darkness in Mirkwood, for though many deemed that it was wrought by the Ringwraiths, he feared that it was indeed the first shadow of Sauron returning; and he went to Dol Guldur, and the Sorcerer fled from him, and there was a watchful peace for a long while. - The Silmarillion, Of the Rings of Power and the Third Age

The Watchful Peace is a very interesting time, as it is when Legolas is born. Tolkien never gives us his birthdate, but the evidence speaks for itself.

Let's start with Legolas's name:

Legolas means 'green-leaves', a woodland name -- dialectal form of pure Sindarin laegolas: *lassë (High-elven lasse, S. las(s) 'leaf'; *gwa-lassa/*gwa-lassië 'collection of leaves, folliage' (H.E. laica, S. laeg (seldom used, usually replaced by calen), woodland leg-). - Letter 211

Legolas's name is the only case we know of where a Sindarin word is Silvanized, instead of the other way around. Interestingly, Mirkwood's two names use the common calen, instead of laeg: Eryn Galen and Eryn Lasgalen.

(The only other time we have laeg used is for the Laegrim, or Green-elves. Both they and the Silvan elves are Nandor)

Why the Silvan emphasis on Legolas's name? Oropher and Thranduil wanted to return to a more 'Silvan' way of life; but Sindarin was the main language, and they didn't Slivanize the names of the realm!

Tolkien provides the answer.

Legolas is translated Greenleaf (II 106, 154) a suitable name for a Woodland Elf, though one of royal and originally Sindarin line. 'Fiery locks' is entirely inappropriate: he was not a balrog! I think an investigator, not led astray by my supposed devotion to A-S, might have perceived the relation of the element -las to lassi 'leaves', in Galadriel's lament, lasse-lanta 'leaf-fall' = autumn. III 386; and Eryn Lasgalen III 375. 'Technically' Legolas is a compound (according to rules) of S. laeg 'viridis' fresh and green, and go-lass 'collection of leaves, foliage'. - Letter 297

As we will go over, Legolas continually refers to himself as a Silvan elf. Here, Tolkien calls him a Wood-elf. He also says that Legolas comes from an “originally Sindarin line”. Originally, as in it didn't stay a purely Sindarin line – otherwise the line would be, “one of royal and Sindarin line.”

Legolas's mother was Silvan. Legolas is raised as a Silvan elf.

Knowing his family history, Legolas's personality is almost mind blowing.

First, though, the proof of Legolas identifying as Silvan.

“That is true,” said Legolas. “But the Elves of this land were of a race strange to us of the silvan folk, and the trees and the grass do not now remember them: Only I hear the stones lament them: deep they delved us, fair they wrought us, high they builded us; but they are gone. They are gone. They sought the Havens long ago.” - Lord of the Rings, The Ring Goes South 

“Yes, they are Elves,” said Legolas; “and they say that you breathe so loud that they could shoot you in the dark.” Sam hastily put his hand over his mouth. “But they say also that you need have no fear. They have been aware of us for a long while. They heard my voice across the Nimrodel, and knew that I was one of their Northern kindred, and therefore they did not hinder our crossing; and afterwards they heard my song.” 

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“Welcome!” the Elf then said again in the Common Language, speaking slowly. “We seldom use any tongue but our own; for we dwell now in the heart of the forest, and do not willingly have dealings with any other folk. Even our own kindred in the North are sundered from us. But there are some of us still who go abroad for the gathering of news and the watching of our enemies, and they speak the languages of other lands. I am one. Haldir is my name. My brothers, Rúmil and Orophin, speak little of your tongue. 

But we have heard rumours of your coming, for the messengers of Elrond passed by Lórien on their way home up the Dimrill Stair. We had not heard of hobbits, or halflings, for many a long year, and did not know that any yet dwelt in Middle-earth. You do not look evil! And since you come with an Elf of our kindred, we are willing to befriend you, as Elrond asked; though it is not our custom to lead strangers through our land. But you must stay here tonight. How many are you?” 

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“I am an Elf and a kinsman here,” said Legolas, becoming angry in his turn. - Lord of the Rings, Lothlórien

“Our Northern kindred” is a direct reference to the Silvan elves. There are only a few Sindarin elves in comparison to the Silvan, and Haldir and Legolas are talking generally. Also, Haldir is clearly not a noble. He would not be saying “our” in reference to Celeborn's family.

Legolas also says, “I am an Elf and a kinsman here,”. He is stressing his connection to Haldir as a fellow Silvan elf.

Gwed believes that Legolas is referring to his kinship with Celeborn, in this line. However, the connection this scene repeatedly stresses is the Silvan one.

Frodo also notes that Legolas is different from all of the other elves he's met:

He then pointed out and named those whom Frodo had not met before. There was a younger dwarf at Glóin's side: his son Gimli. Beside Glorfindel there were several other counsellors of Elrond's household, of whom Erestor was the chief; and with him was Galdor, an Elf from the Grey Havens who had come on an errand from Círdan the Shipwright. There was also a strange Elf clad in green and brown, Legolas, a messenger from his father, Thranduil, the King of the Elves of Northern Mirkwood. - Lord of the Rings, The Council of Elrond

And Gimli also calls Legolas a wood elf:

Legolas: “I could have been happy here, if I had come in days of peace.”  

“I dare say you could,” snorted Gimli. “You are a Wood-elf, anyway, though Elves of any kind are strange folk. - Lord of the Rings, The White Rider

Now, Legolas's age. How do we know he was born in the Watchful Peace? The essay Laws and Customs Among the Eldar tells us that elves control when they procreate, and that they try to only do so during peaceful times.

Legolas himself gives us the answer, by process of elimination.

He has little knowledge of the Noldor and Hollin:

“That is true,” said Legolas. “But the Elves of this land were of a race strange to us of the silvan folk, and the trees and the grass do not now remember them: Only I hear the stones lament them: deep they delved us, fair they wrought us, high they builded us; but they are gone. They are gone. They sought the Havens long ago.” - Lord of the Rings, The Ring Goes South

He has little knowledge of Fangorn:

“You have journeyed further than I,” said Legolas. “I have heard nothing of this in my own land, save only songs that tell how the Onodrim, that Men call Ents, dwelt there long ago; for Fangorn is old, old even as the Elves would reckon it.” - Lord of the Rings, The Riders of Rohan

He has never been to Lothlórien:

“There lie the woods of Lothlórien!” said Legolas. “That is the fairest of all the dwellings of my people. There are no trees like the trees of that land. For in the autumn their leaves fall not, but turn to gold. Not till the spring comes and the new green opens do they fall, and then the boughs are laden with yellow flowers; and the floor of the wood is golden, and golden is the roof, and its pillars are of silver, for the bark of the trees is smooth and grey. So still our songs in Mirkwood say. My heart would be glad if I were beneath the eaves of that wood, and it were springtime!” 

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“It is long since any of my own folk journeyed hither back to the land whence we wandered in ages long ago,” said Legolas, “but we hear that Lórien is not yet deserted, for there is a secret power here that holds evil from the land. Nevertheless its folk are seldom seen, and maybe they dwell now deep in the woods and far from the northern border.” 

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“Here is Nimrodel!” said Legolas. “Of this stream the Silvan Elves made many songs long ago, and still we sing them in the North, remembering the rainbow on its falls, and the golden flowers that floated in its foam. All is dark now and the Bridge of Nimrodel is broken down. I will bathe my feet, for it is said that the water is healing to the weary.” He went forward and climbed down the deep-cloven bank and stepped into the stream. 

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“I will climb up,” said Legolas. “I am at home among trees, by root or bough, though these trees are of a kind strange to me, save as a name in song. Mellyrn they are called, and are those that bear the yellow blossom, but I have never climbed in one. I will see now what is their shape and way of growth.” - Lord of the Rings, Lothlórien

Most tellingly, he only knows songs and tales of the Balrog's awakening:

“Do you hear the voice of Nimrodel?” asked Legolas. “I will sing you a song of the maiden Nimrodel, who bore the same name as the stream beside which she lived lung ago. It is a fair song in our woodland tongue; but this is how it runs in the Westron Speech, as some in Rivendell now sing it.” In a soft voice hardly to be heard amid the rustle of the leaves above them he began: 

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The voice of Legolas faltered, and the song ceased. “I cannot sing any more,” he said. “That is but a part, for I have forgotten much. It is long and sad, for it tells how sorrow came upon Lothlórien, Lórien of the Blossom, when the Dwarves awakened evil in the mountains.” 

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“I said not so; yet evil came,” answered Legolas sadly. “Then many of the Elves of Nimrodel's kindred left their dwellings and departed and she was lost far in the South, in the passes of the White Mountains; and she came not to the ship where Amroth her lover waited for her. But in the spring when the wind is in the new leaves the echo of her voice may still be heard by the falls that bear her name. And when the wind is in the South the voice of Amroth comes up from the sea; for Nimrodel flows into Silverlode, that Elves call Celebrant, and Celebrant into Anduin the Great. and Anduin flows into the Bay of Belfalas whence the Elves of Lórien set sail. But neither Nimrodel nor Amroth ever came back. 

It is told that she had a house built in the branches of a tree that grew near the falls; for that was the custom of the Elves of Lórien, to dwell in the trees, and maybe it is so still. Therefore they were called the Galadhrim, the Tree-people. Deep in their forest the trees are very great. The people of the woods did not delve in the ground like Dwarves, nor build strong places of stone before the Shadow came.” - Lord of the Rings, Lothlórien

Though Legolas never explicitly states he was not alive, the style of his narration speaks for itself. He starts the tale by referencing a well known song; a song which he cannot remember the entirety of. He then goes on to tell what happened in a very basic and impersonal way, as if he is reciting a tale. It is the same style and tone he uses to describe the Galadhrim, and we know he has never met any of them. Nor does he mention anything about how the events effected his own realm – how they found out, what the reaction was, if fear increased in them, etc. Legolas would have that experience to call on if he had been alive, and he has shown he does not mind sharing personal information with the Fellowship.

Legolas's last line. He is stating a bit of his own realms history, saying the Silvan elves had never lived under stone until Sauron's return (Sauron is often called “the Shadow”, see various quotes above).

There are several other clues in the text as to Legolas's age, as well.

“It is old, very old,” said the Elf. “So old that almost I feel young again, as I have not felt since I journeyed with you children. It is old and full of memory. I could have been happy here, if I had come in days of peace.” - Lord of the Rings, The White Rider

Legolas says he has not felt young since beginning the Quest, meaning he felt young before hand.

“Five hundred times have the red leaves fallen in Mirkwood in my home since then,” said Legolas, “and but a little while does that seem to us.” - Lord of the Rings, The King of the Golden Hall 

“These are the strangest trees that ever I saw,” he said; “and I have seen many an oak grow from acorn to ruinous age. I wish that there were leisure now to walk among them: they have voices, and in time I might come to understand their thought.” - Lord of the Rings, The Road to Isengard

Some have taken these two quotes (especially the second one) to mean Legolas is several thousand years old. However, that logic does not hold up. The average life span of most oak trees is 200 - 400 years (source). LotR takes place in TA 3018. The Watchful Peace ended in TA 2460. If Legolas was born in that last year, he would be 558 years old. If he was born in the first year, he would be 955 years old. Most likely, he was born somewhere in the middle of the Watchful Peace.

Even with the youngest number (558), Legolas would still have seen the leaves fall 500 times, and several oak trees die. These two quotes do not negate Legolas having a young age.

You may be wondering what makes Legolas's personality so remarkable. I am going to summarize him.

Legolas sounds like a captain at times and is capable of leading, but he prefers to follow and be the support. He is loyal. He is humble, never mentioning his heritage, and introducing himself as merely one of the Fellowship. He is generally light-hearted, yet serious when he needs to be, and quick to defend and forgive. He is open-hearted, selfless, and kind. He expresses sadness and fear, but never lets it control him. He is sassy, fanciful, and dramatic; and yet realistic about the situations he is in. His curiosity is insatiable. Throughout all of his words and actions, there is an undercurrent of steadiness. He has some measure of foresight, some wisdom (especially compared to Gimli and the hobbits), and some insight into the Unseen forces at work (see here). He is open-minded about men, though not dwarves.

You saw above his ignorance to many things. Thranduil kept Legolas protected and sheltered, never telling him any personal history, or sharing any personal grudges or trauma. All Legolas knows is the songs and tales of his people.

TA 2460: The Watchful Peace ends. Sauron returns with increased strength to Dol Guldur. 

TA 2463: The White Council is formed. - Lord of the Rings, Appendix B 

But at length the Shadow returned and its power increased; and in that time was first made the Council of the Wise that is called the White Council, and therein were Elrond and Galadriel and Círdan, and other lords of the Eldar, and with them were Mithrandir and Curunír. - The Silmarillion, Of the Rings of Power and the Third Age

Sauron returns to Dol Guldur even stronger. As his strength increases, so does the darkness and fell creatures of Mirkwood.

The White Council is formed in response, though they still do not know for sure if the dark power is Sauron. Was Thranduil one of those other elven-lords? We know that he was not a member in TA 2941, when the third meeting happened; because he is present for all the time Gandalf is not, in the quest for Erebor.

So, was Thranduil ever a member? Did he quit? Or was he not invited? We will never know for sure, but guesses can be made.

Mithrandir was closest in friendship with the Eldar, and wandered mostly in the West and never made for himself any lasting abode. - Lord of the Rings, Appendix B

Judging by Legolas's interactions with and reactions to Gandalf in LotR, they had clearly met before (we will talk later about the Gollum situation). Being the only other elven-ruler, Thranduil must have gotten an invitation.

So. It has been three years since the end of the Watchful Peace, and the return of the darkness in Mirkwood. Thranduil would be looking for strategy and information. However, this is politics, and political undercurrents always have to show up and get in the way.

Galadriel: “I it was who first summoned the White Council. And if my designs had not gone amiss, it would have been governed by Gandalf the Grey, and then mayhap things would have gone otherwise.” - Lord of the Rings, The Mirror of Galadriel 

And Curunír (that was Saruman the White) was chosen to be their chief, for he had most studied the devices of Sauron of old. Galadriel indeed had wished that Mithrandir should be the Lead of the Council, and Saruman begrudged them that, for his pride and desire of mastery was grown great; but Mithrandir refused the office, since he would have no ties and no allegiance, save to those who sent him, and he would abide in no place nor be subject to any summons. - The Silmarillion, Of the Rings of Power and the Third Age

There was tension in the White Council from the very beginning. They weren't all of the same mindset, and the battle for dominance and power was the first thing on the agenda.

While Thranduil doesn't hate Celeborn and Galadriel as much as his father did (he lets them into his realm and doesn't poison Legolas against them); he is not in a position to think highly of them, nor any of the other elves. He would have no sympathy or patience for petty squabbles, his land was being overtaken by darkness!

It would be clear from the beginning that while the others were worried about the Shadow, they did not particularly care about the Woodland Realm. The matter of the Three Rings would also be a sore point.

Throughout the Third Age the guardianship of the Three Rings was known only to those who possessed them. But at the end it became known that they had been held at first by the three greatest of the Eldar: Gil-galad, Galadriel, and Círdan. Gil-galad before he died gave his ring to Elrond; Círdan later surrendered his to Mithrandir. - Lord of the Rings, Appendix B 

Of the Three Rings that the Elves had preserved unsullied no open word was ever spoken among the Wise, and few even of the Eldar knew where they were bestowed. Yet after the fall of Sauron their power was ever at work, and where they abode there mirth also dwelt and all things were unstained by the griefs of time. Therefore ere the Third Age was ended the Elves perceived that the Ring of Sapphire was with Elrond, in the fair valley of Rivendell, upon whose house the stars of heaven most brightly shone; whereas the Ring of Adamant was in the Land of Lórien where dwelt the Lady Galadriel. A queen she was of the woodland Elves, the wife of Celeborn of Doriath, yet she herself was of the Noldor and remembered the Day before days in Valinor, and she was the mightiest and fairest of all the Elves that remained in Middle-earth. But the Red Ring remained hidden until the end, and none save Elrond and Galadriel and Círdan knew to whom it had been committed. 

Thus it was that in two domains the bliss and beauty of the Elves remained still undiminished while that Age endured: in Imladris; and in Lothlórien, the hidden land between Celebrant and Anduin, where the trees bore flowers of gold and no Orc or evil thing dared ever come. - The Silmarillion, Of the Rings of Power and the Third Age

The darkness was centered in Thranduil's realm, and yet he was not given a Ring of Power to fight it. Meanwhile, he would see the circumstantial evidence of Elrond and Galadriel each having one. Add on top of this that the others thought their power plays were more important; it is likely that Thranduil saw himself as once again being cheated and dismissed.

Many years pass before the White Council meets again.

c. TA 2480: Orcs begin to make secret strongholds in the Misty Mountains so as to bar all the passes into Eriador. Sauron begins to people Moria with his creatures. 

TA 2509: Celebrían, journeying to Lórien, is waylaid in the Redhorn Pass, and receives a poisoned wound. 

TA 2510: Celebrían departs over sea. 

TA 2740: Orcs renew their invasions of Eriador. 

TA 2770: Smaug the Dragon descends on Erebor. Dale destroyed. 

TA 2850: Gandalf again enters Dol Guldur, and discovers that its master is indeed Sauron,[cut]. 

TA 2851: The White Council meets. Gandalf urges an attack on Dol Guldur. Saruman overrules him.1 - Lord of the Rings, Appendix B 

Now the Shadow grew ever greater, and the hearts of Elrond and Mithrandir darkened. Therefore on a time Mithrandir at great peril went again to Dol Guldur and the pits of the Sorcerer, and he discovered the truth of his fears, and escaped. - The Silmarillion, Of the Rings of Power and the Third Age

The part of App B I give is only a fraction of the events that happen during this period. However, it is enough to show that 388 years of increasing darkness and tragedy happen, and the White Council does nothing. They don't even meet. It is very likely that Thranduil has already turned his back on the White Council by the second meeting.

TA 2941: The White Council meets; Saruman agrees to an attack on Dol Guldur,[cut]. Sauron having made his plans abandons Dol Guldur. The Battle of the Five Armies in Dale. - Lord of the Rings, Appendix B 

But ever the shadow in Mirkwood grew deeper, and to Dol Guldur evil things repaired out of all the dark places of the world; and they were united again under one will, and their malice was directed against the Elves and the survivors of Númenor. Therefore at last the Council was again summoned and the lore of the Rings was much debated; but Mithrandir spoke to the Council, saying: [cut] 

Therefore, for the last time, he aided the Council, and they put forth their strength; and they assailed Dol Guldur, and drove Sauron from his hold, and Mirkwood for a brief while was made wholesome again. - The Silmarillion, Of the Rings of Power and the Third Age

We know that Thranduil was not a part of the White Council by this time, since we have reached the Quest for Erebor. We are told that the Shadow continued to grow, and even started to attack the Free Peoples. Thranduil's realm would have received much of this, being in the same forest. Thankfully they receive a slight reprieve, when Sauron flees to Mordor.

Now, curiously, Gollum comes into the picture.

TA 2944: Gollum leaves the Mountains and begins his search for the 'thief' of the Ring. - Lord of the Rings, Appendix B 

“From the first my heart misgave me, against all reason that I knew,” said Gandalf, “and I desired to know how this thing came to Gollum, and how long he had possessed it. So I set a watch for him, guessing that he would ere long come forth from his darkness to seek for his treasure. He came, but he escaped and was not found. And then alas! I let the matter rest, watching and waiting only, as we have too often done.” - Lord of the Rings, The Council of Elrond 

Gandalf: “His longing for the Ring proved stronger than his fear of the Orcs, or even of the light. After a year or two he left the mountains. [cut] 

He found his way into Mirkwood, as one would expect. [cut] 

He was not daunted by the distance, I am sure. No, something else drew him away. So my friends think, those that hunted him for me. The Wood-elves tracked him first, an easy task for them, for his trail was still fresh then. Through Mirkwood and back again it led them, though they never caught him. The wood was full of the rumour of him, dreadful tales even among beasts and birds. The Woodmen said that there was some new terror abroad, a ghost that drank blood. It climbed trees to find nests; it crept into holes to find the young; it slipped through windows to find cradles. 

But at the western edge of Mirkwood the trail turned away. It wandered off southwards and passed out of the Wood-elves’ ken, and was lost. And then I made a great mistake. Yes, Frodo, and not the first; though I fear it may prove the worst. I let the matter be. I let him go; for I had much else to think of at that time, and I still trusted the lore of Saruman. 

Well, that was years ago. I have paid for it since with many dark and dangerous days. The trail was long cold when I took it up again, after Bilbo left here. And my search would have been in vain, but for the help that I had from a friend: Aragorn, the greatest traveller and huntsman of this age of the world.” - Lord of the Rings, The Shadow of the Past

Gandalf asked the Wood-elves to keep an eye out for Gollum, believing he would follow Bilbo's trail. They did so, but did not follow the trail outside of their wood. They only got involved only because Gollum entered their realm.

TA 2951: Sauron sends three of the Nazgûl to reoccupy Dol Guldur. - Lord of the Rings, Appendix B 

Now at that time [3018] the Chieftain of the Ringwraiths dwelt in Minas Morgul with six companions, while the second to the Chief, Khamûl the Shadow of the East, abode in Dol Guldur as Sauron's lieutenant, with one other as his messenger.11 According to the entry in the Tale of Years for 2951 Sauron sent three, not two, of the Nazgûl to reoccupy Dol Guldur. - Unfinished Tales, The Hunt for the Ring

One of the Nazgûl must have left Dol Guldur between 2951 and 3018. However, the presence of any Nazgûl would have returned the darkness to Mirkwood. The elves had had a reprieve of only ten years.

Anborn: “A large squirrel, maybe. Perhaps under the shadow of the Unnamed some of the beasts of Mirkwood are wandering hither to our woods. They have black squirrels there, 'tis said.” 

“Perhaps,” said Faramir. “But that would be an ill omen, if it were so. We do not want the escapes of Mirkwood in Ithilien.” - Lord of the Rings, The Window on the West

Even in Gondor there are tales of the horrors in Mirkwood.

Also:

He lifted his eyes across the river and all the light went out, and he was back again in the world he knew. Beyond the river the land appeared flat and empty, formless and vague, until far away it rose again like a wall, dark and drear. The sun that lay on Lothlórien had no power to enlighten the shadow of that distant height. 

“There lies the fastness of Southern Mirkwood,” said Haldir. “It is clad in a forest of dark fir, where the trees strive one against another and their branches rot and wither. In the midst upon a stony height stands Dol Guldur, where long the hidden Enemy had his dwelling. We fear that now it is inhabited again, and with power sevenfold. A black cloud lies often over it of late.” - Lord of the Rings, Lothlórien

This is the effect of the Nazgûl.

TA 2953: Last meeting of the White Council. They debate the Rings. - Lord of the Rings, Appendix B

The White Council has its fourth and final meeting; which we know Thranduil was not a part of.

TA 3001: Gandalf seeks for news of Gollum and calls on the help of Aragorn. 

TA 3009: Gandalf and Aragorn renew their hunt for Gollum at intervals during the next eight years, searching in the vales of Anduin, Mirkwood, and Rhovanion to the confines of Mordor. 

TA 3017: [Gollum] is taken by Aragorn in the Dead Marshes, and brought to Thranduil in Mirkwood. - Lord of the Rings, Appendix B 

Aragorn: “I deemed it the worst part of all my journey, the road back, watching him day and night, making him walk before me with a halter on his neck, gagged, until he was tamed by lack of drink and food, driving him ever towards Mirkwood. I brought him there at last and gave him to the Elves, for we had agreed that this should be done; and I was glad to be rid of his company, for he stank. 

[cut] 

Still I for one am glad that he is safely kept by the watchful Elves of Mirkwood.” - Lord of the Rings, The Council of Elrond

Why Mirkwood? is a question many fans have asked. It is clear why Gondor wasn't an option – no one got along with Denethor. Lórien is closed off from the outside world, and Rivendell gets too much traffic. Also, neither realm seems to be equipped to hold prisoners.

Most importantly, secrecy was paramount. Not only does Mirkwood have a state-of-the-art dungeon, the wood-elves were already involved. They didn't need to be told anything, or convinced that Gollum was a threat – they already knew. We will see in a moment that Gandalf and Aragorn didn't tell anyone, even Thranduil and Legolas, about Gollum's connection to the Ring.

TA June 20: Sauron attacks Osgiliath. About the same time Thranduil is attacked, and Gollum escapes. - Lord of the Rings, Appendix B 

“Alas! alas!” cried Legolas, and in his fair elvish face there was great distress. “The tidings that I was sent to bring must now be told. They are not good, but only here have I learned how evil they may seem to this company. Sméagol, who is now called Gollum, has escaped.” 

[cut] 

“Not through lack of watchfulness,” said Legolas; “but perhaps through over-kindliness. And we fear that the prisoner had aid from others, and that more is known of our doings than we could wish. We guarded this creature day and night, at Gandalf's bidding, much though we wearied of the task. But Gandalf bade us hope still for his cure, and we had not the heart to keep him ever in dungeons under the earth, where he would fall back into his old black thoughts.” - Lord of the Rings, The Council of Elrond

Gandalf told the wood-elves to guard Gollum, and that Gollum could perhaps be healed. It is clear by these two passages that Thranduil knew nothing about Gollum's history or importance.

[cut] and Legolas continued. “In the days of fair weather we led Gollum through the woods; and there was a high tree standing alone far from the others which he liked to climb. Often we let him mount up to the highest branches, until he felt the free wind; but we set a guard at the tree's foot. One day he refused to come down, and the guards had no mind to climb after him: he had learned the trick of clinging to boughs with his feet as well as with his hands; so they sat by the tree far into the night. 

It was that very night of summer, yet moonless and starless, that Orcs came on us at unawares. We drove them off after some time; they were many and fierce, but they came from over the mountains, and were unused to the woods. When the battle was over, we found that Gollum was gone, and his guards were slain or taken. It then seemed plain to us that the attack had been made for his rescue, and that he knew of it beforehand. How that was contrived we cannot guess; but Gollum is cunning, and the spies of the Enemy are many. The dark things that were driven out in the year of the Dragon's fall have returned in greater numbers, and Mirkwood is again an evil place, save where our realm is maintained. 

We have failed to recapture Gollum. We came on his trail among those of many Orcs, and it plunged deep into the Forest, going south. But ere long it escaped our skill, and we dared not continue the hunt; for we were drawing nigh to Dol Guldur, and that is still a very evil place; we do not go that way.” - Lord of the Rings, The Council of Elrond

Legolas speaks like a Captain here, reporting Gollum's escape. He also tells us about the state of Mirkwood – the Shadow is back and stronger than ever before, and pulled off a surprise attack on the elves. Gollum's guards were not just killed; some were taken prisoner.

We get more information on this attack in Unfinished Tales, The Hunt for the Ring:

Gollum, however, was before long captured by Aragorn, and taken to Northern Mirkwood; and though he was followed, he could not be rescued before he was in safe keeping. 

[cut] 

So it was that Sauron prepared two strokes - in which many saw the beginnings of the War of the Ring. They were made together. The Orcs assailed the realm of Thranduil, with orders to recapture Gollum; and the Lord of Morgul was sent forth openly to battle against Gondor. These things were done towards the end of June 3018. 

[cut] 

About the twenty-second of July they met their companions, the Nazgûl of Dol Guldur, in the Field of Celebrant. There they learned that Gollum had eluded both the Orcs that recaptured him, and the Elves that pursued them, and had vanished.2 

[cut] 

The whole journey, on foot, was not much short of nine hundred miles, and this Aragorn accomplished with weariness in fifty days, reaching Thranduil on the twenty-first of March.6 

It is thus most likely that the first news of Gollum would be learned by the servants of Dol Guldur after Aragorn entered the Forest; for though the power of Dol Guldur was supposed to come to an end at the Old Forest Road, its spies were many in the wood. The news evidently did not reach the Nazgûl commander of Dol Guldur for some time, and he probably did not inform Barad-dûr until he had tried to learn more of Gollum's whereabouts. It would then no doubt be late in April before Sauron heard that Gollum had been seen again, apparently captive in the hands of a Man. This might mean little. Neither Sauron nor any of his servants yet knew of Aragorn or who he was. But evidently later (since the lands of Thranduil would now be closely watched), possibly a month later, Sauron heard the disquieting news that the Wise were aware of Gollum, and that Gandalf had passed into Thranduil's realm. Sauron must then have been filled with anger and alarm. He resolved to use the Ringwraiths as soon as he could, for speed rather than secrecy was now important. Hoping to alarm his enemies and disturb their counsels with the fear of war (which he did not intend to make for some time), he attacked Thranduil and Gondor at about the same time.7 

7 Both here and in the Tale of Years the assault on Osgiliath is dated the 20th of June. 

[cut] 

It seems clear that pursued both by Elves and Orcs Gollum crossed the Anduin, probably by swimming, and so eluded the hunt of Sauron; but being still hunted by Elves, and not yet daring to pass near Lórien (only the lure of the Ring itself made him dare to do this afterwards), he hid himself in Moria.10

Gollum was not still being hunted by the elves, according to Legolas in LotR, so this last part of the quote must be discarded. The rest of this tells us just how important, in the scheme of things, this attack was.

What was going on in Mirkwood, during the War of the Ring?

The hobbits had been nearly two months in the House of Elrond, and November had gone by with the last shreds of autumn, and December was passing, when the scouts began to return. [cut] Many had gone east and south; and some of these had crossed the Mountains and entered Mirkwood, [cut]. - Lord of the Rings, The Ring Goes South

Thranduil sent Legolas to deliver a message, and now he most likely finds out Legolas is going on a quest to destroy the One Ring.

The realm of Thranduil was invaded, and there was long battle under the trees and great ruin of fire; but in the end Thranduil had the victory. - Lord of the Rings, Appendix B 

TA March 15, 3019: Battle of the Pelennor. [cut] Battle under the trees in Mirkwood; Thranduil repels the forces of Dol Guldur. - Lord of the Rings, Appendix B

Thranduil and his people fought a day-long and very difficult battle, but had the victory. This is the Woodland Realm's only battle during the War of the Ring.

And on the day of the New Year of the Elves, Celeborn and Thranduil met in the midst of the forest; and they renamed Mirkwood Eryn Lasgalen, The Wood of Greenleaves. Thranduil took all the northern region as far as the mountains that rise in the forest for his realm; and Celeborn took all the southern wood below the Narrows, and named it East Lórien; all the wide forest between was given to the Beornings and the Woodmen. - Lord of the Rings, Appendix B 

TA April 6, 3019: Meeting of Celeborn and Thranduil. - Lord of the Rings, Appendix B

We can assume that Thranduil and Celeborn's meeting was civil but businesslike, due to their history.

What happens during the Fourth Age? Does Thranduil sail? The ending of the tale has come.

First, we know that Thranduil had the sea longing. He lived in both the refugee camp on the island of Balar and in Lindon, before moving to the Greenwood.

Also, the Silvan elves were able to sail (we know this because of Nimrodel and her kin), and it was possible for them to also get the sea longing:

The Silvan Elves (it is remarked here) “were never wholly free of an unquiet and a yearning for the Sea which at times drove some of them to wander from their homes.” - Unfinished Tales, The History of Galadriel and Celeborn, Amroth and Nimrodel

Some fans have thought that this is invalidated by the fact that a quote above says Oropher and the others “came from Doriath after its ruin and had no desire to leave Middle-earth, [cut]. They wished indeed to become Silvan folk and to return, as they said, to the simple life natural to the Elves before the invitation of the Valar had disturbed it.”

However, this does not invalidate the sea longing or the possible sailing of Thranduil and his people. Like with Legolas, the sea longing had to be awoken in the Silvan elves. Also, Oropher migrated during the first part of the Second Age. He is no longer alive, and the situation is very different in the Fourth Age. The motivations of past actions cannot always be used to explain present actions.

But after the passing of Galadriel in a few years Celeborn grew weary of his realm and went to Imladris to dwell with the sons of Elrond. In the Greenwood the Silvan Elves remained untroubled, but in Lórien there lingered sadly only a few of its former people, and there was no longer light in Caras Galadhon. - Lord of the Rings, Appendix B 

Fo.A. 15: King Elessar rides north, and dwells for a while by Lake Evendim. He comes to the Brandywine Bridge, and there greets his friends. He gives the Star of the Dúnedain to Master Samwise, and Elanor is made a maid of honour to Queen Arwen. - Lord of the Rings, Appendix B 

Sam: “Well dear, Celeborn still lives there among his trees and his Elves, and there I don't doubt your flower grows still. 

[cut] 

And so I think Celeborn is still happy among his trees, in an Elvish way. His time hasn't come, and he isn't tired of his land yet. When he is tired he can go.” - Sauron Defeated, Part One: The End of the Third Age, The Epilogue

Since the epilogue takes place in Fo.A. 15, we know Celeborn left Lórien some time after that. This takes place in the beginning of the Fourth Age, so we know that the above line about the Woodland Realm refers to this period of time.

There, though Elrond had departed, his sons long remained, together with some of the High-elven folk. It is said that Celeborn went to dwell there after the departure of Galadriel; but there is no record of the day when at last he sought the Grey Havens, and with him went the last living memory of the Elder Days in Middle-earth. - Lord of the Rings, Prologue

Celeborn did not remain forever; at some point he sailed, and Elladan and Elrohir died (see here). When?

Círdan's history says that it is his fate to stay in Middle-earth until the last ships sails. We know that he is still in Middle-earth in Fo.A. 61, because Sam sails from the Grey Havens (App B).

However, the situation is very different in Fo.A. 120:

“Lady Undómiel,” said Aragorn, “the hour is indeed hard, yet it was made even in that day when we met under the white birches in the garden of Elrond where none now walk.” - Lord of the Rings, Appendix A 

[cut] and passed away to the land of Lórien, and dwelt there alone under the fading trees until winter came. Galadriel had passed away and Celeborn also was gone, and the land was silent. - Lord of the Rings, Appendix A

Both Rivendell and Lórien are completely deserted by the time Aragorn and Arwen die. Celeborn, Elladan, and Elrohir are all gone. Celeborn sailed from the Grey Havens.

Legolas's actions at this time are very telling:

Fo.A. 120: Then Legolas built a grey ship in Ithilien, and sailed down the Anduin and so over Sea; and with him, it is said, went Gimli the Dwarf. - Lord of the Rings, Appendix B

Legolas builds his own ship, and sails from Ithilien.

This does not make sense if Thranduil and Círdan were still in Middle-earth. Legolas's actions and personality tell us that he was a young elf, sheltered and protected by his father. We also know that family and relationships matter greatly to elves:

They had few children, but these were very dear to them. Their families, or houses, were held together by love and a deep feeling for kinship in mind and body; and the children needed little governing or teaching. - Morgoth's Ring, Laws and Customs Among the Eldar 

The sentiment of affection for sister's children was strong among all peoples of the Third Age, but less so among Dwarves than Men or Elves among whom it was strongest. - The Peoples of Middle-earth, Durin's Folk, The Making of Appendix A

It is inconceivable that Legolas would leave without saying goodbye to his father. We see with Arwen and Elrond that the idea of eternal separation is unbearable, and causes immense grief. Also, it would be a lot easier to travel to the Grey Havens and get on a pre-made ship with other elves.

So, what is our missing piece of the puzzle?

The fading.

And Gandalf said: “This is your realm, and the heart of the greater realm that shall be. The Third Age of the world is ended, and the new age is begun; and it is your task to order its beginning and to preserve what may be preserved. For though much has been saved, much must now pass away; and the power of the Three Rings also is ended. And all the lands that you see, and those that lie round about them, shall be dwellings of Men. For the time comes of the Dominion of Men, and the Elder Kindred shall fade or depart.” - Lord of the Rings, The Steward and the King 

Haldir: “Some there are among us who sing that the Shadow will draw back and peace shall come again. Yet I do not believe that the world about us will ever again be as it was of old, or the light of the Sun as it was aforetime. For the Elves, I fear, it will prove at best a truce, in which they may pass to the Sea unhindered and leave the Middle-earth for ever.” - Lord of the Rings, Lothlórien 

Galadriel: “Yet if you succeed, then our power is diminished, and Lothlórien will fade, and the tides of Time will sweep it away. We must depart into the West, or dwindle to a rustic folk of dell and cave, slowly to forget and to be forgotten.” - Lord of the Rings, The Mirror of Galadriel 

Treebeard: “It is sad that we should meet only thus at the ending. For the world is changing: I feel it in the water, I feel it in the earth, and I smell it in the air. I do not think we shall meet again.” - Lord of the Rings, Many Partings 

This really marked the beginning of the Dominion of Men, though there was (in our view) a long twilight period between the downfall of Morgoth and the final overthrow of Sauron: lasting, that is, through the Second and Third Ages. - Morgoth's Ring, Athrabeth Finrod ah Andreth, Note 4 

The 'waning' of the Elvish hröar must therefore be part of the History of Arda as envisaged by Eru, and the mode in which the Elves were to make way for the Dominion of Men. The Elves find their supersession by Men a mystery, and a cause of grief; for they say that Men, at least so largely governed as they are by the evil of Melkor, have less and less love for Arda in itself, and are largely busy in destroying it in the attempt to dominate it. - Morgoth's Ring, Athrabeth Finrod ah Andreth, Note 7 

Sam: “You came at the end of a great age, Elanorellë; but though it's over, as we say, things don't really end sharp like that. It's more like a winter sunset. The High Elves have nearly all gone now with Elrond. But not quite all; and those that didn't go will wait now for a while. And the others, the ones that belong here, will last even longer.” - Sauron Defeated, Part One: The End of the Third Age, The Epilogue

The elves didn't have many more centuries to think about sailing, in the Fourth Age. Lórien and Rivendell being completely empty, Legolas building his own ship... it all implies that the elves had only a little time left to continue to live as they had in Middle-earth. Fading meant having your body disappear, and you become an invisible spirit (see Laws and Customs Among the Eldar). The more years that passed, the greater the fading increased; as did the pressure on the elves' to depart.

So. Thranduil must have sailed before Legolas, who had remained for Aragorn (see here).

~*~

Legolas's family history is truly fascinating. I am continually amazed by the depth and detail Tolkien put into Middle-earth. I hope this essay has helped you understand better some of his greatest elves.