The Barddas of Iolo Morganwg, Vol. I., ed. by J. Williams Ab Ithel, , at sacred-texts.com
Before the coming of Christ in the flesh, the Bards solemnized times according to the years of memorial and computation, namely, from the time of Prydain, the son of Aedd the Great, who was famous five hundred and sixty-six years before the birth of Christ in the flesh; and from that time it is usual with the Bards to celebrate the memorial and computation of time in accordance with the years of Christ. Prydain, the son of Aedd the Great, as far as memorial and knowledge go, lived the time mentioned before the birth of Christ, and, according to the conjecture of wise men, and well informed herald-bards, six hundred and fifty years subsequently to the first arrival of the Cymry in the island of Britain. It was thus, one thousand two hundred and six-teen years before the birth of Christ that the nation of the Cymry first came into the island of Britain, and this was called Brut time, because the years of memory and computation were in old times conjecturally reckoned from the time of Brut, 1 which was about a thousand years after the demolition of the tower of Nimrod the Giant, and about two thousand and eight hundred years after the expulsion of Adam and Eve from the garden of Paradise, which occurred five 2 hundred years after God had made this world.
407:1 p. 405 Brut--Brutus, supposed to be the same with Prydain.
407:2 p. 206 Al. "nine."