In Geoffrey of Monmouth's Historia Regum Britanniae, he overthrows his father and reigns as King of Britain for a brief period before his death restores Vortigern to power.
According to the Historia, Vortigern allows Saxons under Hengest and Horsa to settle on the Isle of Thanet, and offers them provisions in exchange for their service as mercenaries.
[3] Another manuscript of the Historia Brittonum (Chronica Minora, Berlin, 1892) follows this with: "if they had kept his command, there is no doubt that they would have obtained whatever they wished through the prayers of St Germanus.”[4] According to the Welsh Triads his bones were buried "in the Chief Ports of this Island".
[5] Three of Vortimer's battle sites are named: the first was on the Darent "super flumen Derguentid'" the second "at the ford called Episford in their language, Rhyd yr Afael in ours 'super vadum quod dicitur in lingua eorum Episford, in nostra autem lingua Rithergabail'"; the third was "by the inscribed stone on the shore of the Gallic Sea 'in campo juxta Lapidem tituli, qui est super ripam Gallici maris'".
Philip Morant tells us that Aldroen, king of Armorica, sent ten thousand troops to Britain under the command of Aurelius Ambrosius.
Peace was eventually brokered between the warring factions by splitting Britain between them: Aurelius ruling the western part of the island, with Vortimer and Vortigern in the east: "divided from one another by... Watling Street".