The Barddas of Iolo Morganwg, Vol. I., ed. by J. Williams Ab Ithel, , at sacred-texts.com
p. 408 p. 409
This is the mode in which the ancient Teachers used to denote the memorial of times; that is, from the arrival of the Cymry in this island, it was the conjecture and memory of country and nation, because there was no privilege attached to the science of memorial and computation before the time of Prydain, the son of Aedd, who was called Dyvnvarth Prydain, Dyvnvarth being his original name. His epoch was about seven hundred years after the arrival of the Cymry in this island; and from his time to the advent of Christ in the flesh there were five hundred and fifty-three years, as told in the memorials of computation and tradition, warranted by the sanction of the Bards of the Isle of Britain, under the penalty of losing privilege and office, and the freedom of plough, and gifts, and of all chattels due in respect of song and poetry. Before the coining of the Cymry into this island, there was hardly anything else remembered and preserved by country and nation. This knowledge is called the memorial of computation, and others call it memorial and computation; thus it is said, that it was in the year of memorial and computation, five hundred and fifty-three, Christ came in the flesh; and this has been kept in practice down to the time. 1
409:1 p. 408 The fragment would appear to be imperfect, unless we read "to this time."