The Barddas of Iolo Morganwg, Vol. I., ed. by J. Williams Ab Ithel, [1862], at sacred-texts.com
The five Ages of Letters. The first was the age of the three letters, which above all represented the Name of God and goodness, and which were a sign of goodness and truth, and understanding and equity, of whatsoever kind they might be. Other things were exhibited under the sign of blazonry in respect of the art of a herald-bard. This is the mode in which they numbered ten according to the three letters, namely, , being put for ten, and after that for the second tenth, that is, a hundred, and for the third tenth, that is, a thousand, and for the fourth tenth, that is, a myriad, and for a million , and for buna , and so on to three , or four or more. According to this arrangement stood for A, that is, the first letter, for B, that is, the second, , the third, , the fourth, , , , , , and , the tenth letter, , the twelfth. This is the first age.
In the second age sixteen letters were arranged, whence literature became more clear. After that, In the third age there were eighteen letters, for the improvement of literature; that is, was put for the second
sound of B; and then the three letters of God's Name were made into ; and the eighteenth letter was , or, according to another form, .
In the fourth age there were twenty-four letters; and the Name of God, according to the arrangement of the third age, was a secret.
The fifth age was, as it is now, that is, there were thirty-eight letters; and the Name of God, according to the arrangement of the third age, was kept a secret.
95:1 p. 94 "Rhiaint was a name given to the sixteen letters, and in the Ancient Secret the Birds of Rhianon:--one letter was called Rhïan, plur. Rhieinau."--Iolo Morganwg, who refers to Llywelyn Sion.
He will buy wine from the vines,
She like Rhianon will give it.
Sion Brwynog, to Rhydderch ap Rhys
of Tregaian and his wife.