Geraint (d. 710 CE; known in Latin as Gerontius) was a King of Dumnonia who ruled in the early eighth century. During his reign, it is believed that Dumnonia came repeatedly into conflict with neighbouring Anglo-Saxon Wessex. Geraint was the last recorded king of a unified Dumnonia, and was called King of the Welsh by the Anglo-Saxon Chronicle. Subsequent kings of Dumnonia (e.g. Doniert, Huwell) reigned over a reducing area that eventually encompassed only a part of Cornwall.
A long and rather acrimonious letter survives addressed to him from Aldhelm on the Easter Problem and the shape of the tonsure. It is clear from this letter that in the later seventh century the Brythons in Cornwall and Devon still observed Easter on the dates that the Celtic church had calculated, at variance with Catholic practice. Geraint ultimately agreed with Aldhelm to comply with Roman practice on these points. According to Florence of Worcester, Geraint was killed after a series of battles that culminated in a victory of the West Saxons under Ine of Wessex in 710 CE. It was probably around this time that Devon was conquered by the West Saxons. After Geraint's death, however, Ine was unable to establish his authority over neighbouring Cornwall; in 722, according to the Annales Cambriae, the Cornish won a battle at Hehil, probably against Wessex.
William F. Skene and other scholars suggest Geraint of Dumnonia be identified as the warrior eulogized in the poem Battle of Llongborth, traditionally ascribed to Llywarch Hen. Other scholars associate the slain man with Geraint ab Erbin, a king said to have lived during the 5th century but of dubious historicity. Skene identifies Llongborth with the 710 battle between Geraint and Ine, and suggests Langport in Somerset as the location of the battle.
(Wikipedia)