The earliest known record of the presence of Elves dates from the 12th century, two or three generations before King Uther Pendragon of Britain. We know they were in Cornwall at the time of King Uther and that they had been there for some time, but that the memory of their arrival was not so distant as to have become legendary.
The story that has come down to us has Laird Brendan commanding a great fleet of white ships that landed all along the western shores of Britain, so numerous that their landing sites stretched from Plymouth to Glasgow. At first, they contended with the Nations of Men, and wars between Men and Elves were terrible indeed. These came to an end in the 17th century, when King Aelfred the Great negotiated the Great Peace. The Elves were given a series of locations—whole regions plus certain forests—known collectively as the Elflaw.
We know from rather late sources that Elves came also to Ireland, Scotland, Brittany, and Galicia. Each land has its own tales and legends, but all speak of a great migration, a period of conflict, and a final settlement between the peoples.
The Elves themselves have their own stories. Their legends tell of a distant land over the Western Ocean, a great chain of islands with a magnificent kingdom of wealth and grace. Its name is variously rendered Limur or Lemuria. Some evil race, a race that many scholars now believe was the Drow, appeared and contended for supremacy on the island. A long war escalated relentlessly until vast powers were being wielded on both sides. Something happened and the main island began to sink. The Drow, if that's who they were, fled—it is unclear whether they went into another dimension or underground or over the sea. The Elves hastily loaded all they could onto their fleet, to go to neighboring islands. Alas, those islands, too, sank beneath the waters. Under the leadership of Laird Brendan, the survivors struck out eastward where some claimed were other lands. After great hardship, they arrived in Altearth.
During the First Dark Ages (ca. 1300-1500), the Elves spread eastward. They tended to migrate in large tribes, moving as a whole people to some new forest. This is how Elves came to live in the Ardennes, the Vosges, and the Black Forest. A second wave occurred during the Dragon Years (1600-1800).
Elves are clans, with a king for every clan. Humans call them kings, anyway, being quite unable to pronounce the Elvish, which varies from clan to clan anyway. Think Magyars or the Irish.
All Elves are nobility. Or none. What matters is the clan, outside of which everything is irrelevant.
Modern scholars argue over this. Was Elvish society like this in Atlantis? Or were the clans a survivors' response to the Years of Wandering?
In any case, Elvish politics are utterly focused on inter-clan rivalries. The conflicts are highly ritualized in which individuals die only rarely. They span the gamut from bridge fights to eating and drinking contests, bards, jousts, etc. Dwarves think it's all damned foolish. Humans are fascinated and have borrowed heavily. Most of the knightly ethos is Elvish in origin.
Most scholars agree that Atlantis sank somewhere around 700 AnUC (ante urbe condite). Elvish legend says different clans escaped in different ships—indeed the clan name is derived from the ship name. This is almost certainly not true but was constructed later to legitimize the rule of certain clans.
There followed the Thousand Year Sail (another Elvish exaggeration), or the Diaspora. The Elves did not actually live the whole time on their unsinkable ships, but they may have gone whole generations at sea. Scholars used to think the Elvish stories to be legendary, with their tales of another world over the sea. Then Columbus showed those tales, at least, were true. Recent undersea archaeology has brought evidence to light that appears to confirm—we have found an entire Elvish ship at Sutton Hoo.
For reasons still quite obscure, the Elves began to come ashore in the 1300s. Some settled in Galicia, Brittany, Cornwall and Ireland. Others landed and headed inland, while still others sailed into the Baltic, the Mediterranean, and even (according to the latest research) the Black Sea (see "The Elves of Trebizond" and "The Volga Elves" by Phillipos Papadopolous, two excellent essays in the otherwise very uneven collection, The Elves of the East, edited by G.N. Abranes.).
All evidence indicates that the Elves ended their Diaspora more or less at once. No one understands why. Elvish legends are patently self-serving. Every Clan claims the same thing: it learned of the dire threat of the Wild in Europa and bravely ended its wanderings to Save the World. These frustratingly opaque stories, draped as they are in Elvish formulaic writing, and coupled with a virtual lack of Human documents from the period, leave us with archeology, which tells us where and sometimes when, but rarely why. Ultimately the Thousand Years remains shrouded in mystery.
The Elves are regarded by Humans and Dwarves alike as unreliable at best, traitorous at worst. Much of this comes from the age of Carolus Magnus--the betrayal at Roncevalles is the most notorious. Their failure to fight in the Padanian Wars, and their inconstancy during the unending struggles along the Rhineland were archetypes of Elf-Human relations. This was sealed and saved in legends and histories, the most important of which is certainly the Song of Roland.
Despite all this, Elves surely do know how to dress up, how to throw a feast or tourney, and are spectacularly brave in single combat. They appear to have no sense of strategy whatsoever, and only the most limited ideas about tactics. There are some bitterly funny jokes among Human soldiers along these lines. There may be jokes among the Dwarves, but no Human would understand them.
Elves have magic, but as with so much else Elvent it seems to be useless to Humans. It appears to be hopelessly domestic: flower breeding, interior decorating, cooking, sound effects and party tricks. They make brilliant weapons of great beauty, but they don't enchant them. Dishonorable. Dwarf-magic won't stick to any Elven weapon, a fact which continues to irritate Dwarves to this day.