Tradition, as recorded in the early manuscripts and later in the folklore of the land, tells us that the Tuatha De Danann ruled Ireland before the coming of Celtic invaders known to us as the Gaels.

Much of that tradition is recorded in the Dinnshenchas or 'History of Places' and the Cóir Anmann or 'Fitness of Names', both learned compilations from the Middle Irish period. A large body of material relating to the Tuatha De Danann is also contained in Lebor Gabála Éirenn, or The book of the Invasions of Ireland,' that remarkable scholar T.F. O'Rahilly11 dates the earliest version of this great work to the first half of the ninth century and asserts that our later manuscript is a highly elaborated and expanded version of that earlier lost manuscript. There is also, unfortunately a great deal of Christian material added to the early sections and while one is aware of an intrusive Christian tone throughout, these additions and emendations are obvious to the reader well acquainted with the underlying tradition.

According to Lebor Gabála five successive groups of invaders occupied Ireland before the coming of the Celtic Gaels. The first three groups are known by the names of their leaders, the last two by tribal names:

1. The Cessair
2. The Partholón
3. The Nemedians
4. The Fir Bolg
5. The Tuatha Dé Danann.