The Barddas of Iolo Morganwg, Vol. I., ed. by J. Williams Ab Ithel, [1862], at sacred-texts.com
Chronological memorial and computation were reckoned from the time of Prydain, son of Aedd the Great, who lived four hundred and eighty years before the time when Christ came in the flesh. When Bran the Blessed, the son of Llyr, had exhibited the faith in Christ to the nation of the Cymry, and made them believers in the island of Britain, they began to compute time according to the years of Christ. Some maintain that every cry of country and Gorsedd ought to be dated from the time of Prydain, that is, according to the custom of the ancient Cymry; others maintain that such
should be done in conjunction with the years of Christ; whilst others will have only the years of Christ.
(Sion Bradford.)