In Geoffrey of Monmouth's Historia Regum Britanniae, Brutus wanders about western Europe, stopping in, amongst other places, Aquitane and Gaul. He vanquished Goffarius, king of the Pictavians at Aquitane, with the help of Corineus, the leader of the people who will become known as the Cornish. The next passage (page 17) reads,
The king [Goffarius] after a narrow escape went to several parts of Gaul, to procure succours among such princes as were related or known to him. At that time Gaul was subject to twelve princes, who with equal authority possess the whole country. These receive him courteously, and promise with one consent to expel the foreigners from Aquitane.
Who were the twelve princes?