All we can be sure of is that someone known as Aneirin lived during the end of the sixth century. He was a poet in the kingdom of Gododdin, and "Y Gododdin" is the best known of his works. In Historia Brittanum he is named as "son of Dwywai" which connects him to the royal houses of the North.

Y Gododdin is composed of a number of elegies for a war band from that place, who fought against English invaders at the Battle of Catraeth (Catterick) around 600 CE. And the honor of these eloquent elegies was well-deserved because the men killed seven times their own number - but were still overpowered and every one of them was slain.

Only one copy of Y Gododdin exists (in the 13th century Book of Aneirin) and this resides in Cardiff's Central Library. That copy was obviously written down well after the original composition, pieced together from a combination of oral traditions and fragmentary copies.

From a bardic perspective, it is interesting to note that both Aneirin's and Taliesin's poems set standards for later styles. The characteristic alliteration and internal rhymes in their verses developed into more complicated forms, such as the cyngharedd, by the 13th century.