Geoffrey Ashe points out that Arthur is said by Geoffrey of Monmouth to have crossed into Gaul twice, once to help a Roman emperor and once to subdue a civil war. Riothamus did both, assuming that he was a king in Britain as well as Armorica. Arthur is also said to have been betrayed by one of his advisers, and Riothamus was betrayed by one of his supposed allies. Finally, the Arthurian romances traditionally recount that King Arthur was carried off to Avalon (called "insula Auallonis" by Geoffrey of Monmouth, the first author to mention the legendary isle) before he died; Riothamus, after his defeat at Déols, was last known to have fled to the kingdom of the Germanic Burgundians, perhaps passing through a town called Avallon (which was within Burgundian territory and not far from Bourges).