After the Dedannans had held sway in Ireland for about two hundred years, they were in their turn conquered by the last and greatest colony of all, the people of Milèd or Milesius, who are commonly known by the name of Milesians, and who are the ancestors of the leading Gaelic families of Ireland. The Milesians defeated the Dedannans in two great battles: one fought at Tailltenn, now Teltown, on the river Blackwater, between Navan and Kells, in Meath; and the other at Druim-Lighean, now Drumleene, about three miles from Lifford, in Donegal.
In the legendary and romantic literature of Ireland, the Dedannans are celebrated as magicians. By the Milesians and their descendants they were regarded as gods, and ultimately, in the imagination of the people, they became what are now in Ireland called "fairies."
After their defeat by the Milesians, they seem to have retired to remote and lonely places; and their reputation as magicians, as well as the obscure and mysterious manner in which they lived, gradually impressed the vulgar with the belief that they were supernatural beings.
The notion was that they lived in splendid palaces in the interior of pleasant green hills. These hills were called sidh (pronounced shee); and hence the Dedannans were called Daoine-sidhe (Deena-shee), or people of the fairy hills; Marcra-sidhe (Markra-shee), fairy cavalcade; and Sluagh-sidhe (Sloo-shee), fairy host.
Of this mysterious race, the following are the principal characters mentioned in these tales.
Mannanan Mac Lir, the Gaelic sea-god. In "Cormac's Glossary" (written a.d. 900), we are told that he was a famous merchant who resided in, and gave name to, Inis-Manann, or the Isle of Man; that he was the best merchant in Western Europe; and that he used to know, by examining the heavens, the length of time the fair and the foul weather would last.
The Dagda, whose name some interpret to mean "the great good fire," so called from his military ardour, who reigned as king of Ireland from a.m. 3370 to 3450.
Angus or Angus Oge, the son of the Dagda, who lived at Brugh or Bruga, on the north shore of the Boyne, a little below the village of Slane. Angus is spoken of as the wisest and the most skilled in magic of all the Dedannan race.
Nuada of the Silver Hand. ([See note 4.])