The Lebor Gabala, Leabhar Gabhala or The Book of the Taking of Ireland is the foundation on which most Irish historians have built and developed their work. The manuscript dates from the 11th to 15 centuries, a narration of the successive invasions of Ireland by earliest settlers. These legends have long been believed and/or written as true history but contemporary scholars view them as myths stemming from racial memories and reconstructions of early tales by Christian scribes. The Lebor Gabala is an essential manuscript for any serious study of ancient Irish history.

You can find it online at
http://members.aol.com/lochlan2/lebor.htm