[1] Studies also suggest that features of this form of poetry are comparable to the ancient Irish versifications and therefore point to an older shared Celtic inheritance.
[1] The composition of cerdd dafod requires strict observance of the rules of cynghanedd: an intricate system of sound arrangement based on stress, alliteration, and internal rhyme within each line.
This was later revised by Dafydd ab Edmwnd who, at an eisteddfod held at Carmarthen around 1450, changed two of Einion's metres to two more complicated versions of his own.
[1] In 1925 the Celtic linguist Sir John Morris-Jones published Cerdd Dafod, an in-depth study of the traditional metres of the cynghanedd and a text now seen as the definitive work on the topic.
The end of the 20th century saw a renaissance in cerdd dafod, especially in the metres known as englyn and cywydd, attributed to the poet Alan Llwyd.