Possibly a purely legendary character, Vortimer was a 5th century Brythonic prince, and war-leader. He is also said to have been the first King of Gwent .

Vortimer first appears in the 9th century Historia Britonum, as the son of Vortigern, who was an historical king of the Britons who allowed the settlement of Saxons in the east of the Island. Vortimer leads the Britons in four battles against the Saxons, finally expelling them. But he dies soon after and Vortigern allows the Saxons to return. Three of the battle sites are named, and appear to have some correspondence with battles in Kent appearing in the Anglo-Saxon chronicle. These chronicles do not name Vortimer, and in fact credit Vortigern as the British leader in one of the battles.

The legendary material in the Historia Britonum was slightly expanded upon in Geoffrey of Monmouth's Historia regum Britanniae, a fictional account of the rulers of Britain. There the Britons abandon Vortigern and elevate Vortimer to be king of Britain. After he has driven out the Saxons, Vortimer is poisoned by his stepmother Rowena (a Saxon) and Vortigern regains the crown.

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