Amongst Einion's surviving poems is an awdl sung in praise of Sir Rhys ap Gruffydd.
Einion's fames lies primarily with his metrical grammar, 'llyfr cerddwriaeth', the earliest of its kind known in Welsh.
Although written in Welsh it is partly an adaption of Latin grammars in use during the early Middle Ages, in particular those of Donatus and Priscianus.
It provides a description of the twenty four metres of the cerdd dafod, how they should be composed and a strict edict on proscribed faults.
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