The Barddas of Iolo Morganwg, Vol. I., ed. by J. Williams Ab Ithel, , at sacred-texts.com
Before the knowledge of letters was obtained, there was no other memorial than vocal song, authorized by three Chairs, and the voice of an efficient Gorsedd. There were three efficient Gorsedds that preserved memorials, namely, the Gorsedd of Bards, the Gorsedd of the court of lord and law, and a conventional Gorsedd of country and nation. And every memorial was efficient that received the countenance of three Gorsedds, of one or other of the three Gorsedds of country and nation; that is, the countenance of the same Gorsedd three times under the proclamation and notice of a year and a day.
When the knowledge of letters was obtained, the preservation of Coelbrens, authorized by an efficient Gorsedd, was imposed upon every Gorsedd whatsoever; and that memorial was called Cyvarwydd, also Cyvarwyddyd.
After that, a knowledge of Plagawd, namely, letter skin, called membrane from the Latin, was obtained. Then all the Gorsedds were required to preserve authorized Rolls, as at present; and, after that, Rolls and Books of paper. Nevertheless, the best is the memorial of the Voice of Gorsedd, because no one can know the usage except in the hearing of country and nation, and there can be no confirmed
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knowledge of what is stated by letter and book, because the memory and recollection of letters cannot have the warranty of the hearing of country and nation--one, any more than another, of the Rolls and Books, which do not agree in their records.