Geraint son of Erbin (Middle Welsh Geraint uab Erbin) is a medieval Welsh poem celebrating the hero Geraint and his deeds at the Battle of Llongborth. The poem consists of three-line englyn stanzas and exists in several versions all in Middle Welsh. The earliest surviving version is in the Black Book of Carmarthen, completed around 1250, though the poem may have been composed in the 10th or 11th century.[1] The poem is significant for its early mention of King Arthur.