The Barddas of Iolo Morganwg, Vol. I., ed. by J. Williams Ab Ithel, , at sacred-texts.com
Another mode for booking sciences were the Peithynvain, 1 that is, they wrote with a steel pencil on both surfaces of the stones, and then put them on a strong cord, or on an iron or brass rod, which passed through the top of every Peithynvaen. These stones were called Coelvain. Another method was that of Howel the Good, devised by Blegywryd, his Clerk, 2 which was this;--they faced the hall of the Prince's court with stones, one side and another of the hall, and on the stones wrote in order, with a strong pencil, the laws which Howel imposed upon the country and nation of the Cymry, an open entrance being left for every man that needed, whatever man he might be, whether a native or a stranger, to proceed into the hall, and to read the law, or to have it read to him. Hence it became customary to inscribe
p. 160 p. 161
a vocal song, a Roll, a poem, the memorial of praiseworthy deeds, and the narration of wisdom, on Peithynvain, and to place them on the face of walls and partitions, or on strings, or iron rods. It was from this also that the practice arose of giving the name of Coelvain to all sciences, of whatsoever kind they were, and to whatsoever things that were inscribed thereon.
King Arthur placed the system of the Round Table, and the praiseworthy deeds of its knights, on plates of brass and tin, in his three principal courts, namely, Caerleon-upon-Usk, Celliwig, 1 and Penrhyn Rhionydd, 2 written with a steel pencil.
159:1 p. 158 Peithynvain is the plural of peithynvaen, (peithyn maen,) the stone of elucidation.
159:2 He was also Archdeacon of Llandaff. Sec Ancient Laws and Institutes of Wales, vol. i. p. 343.
161:1 p. 160 This is supposed to be the same as Pendennis Castle. See Hughes's Horæ Britanicæ, vol. ii. append. iii.