The sources are scattered, diverse and numerous, so they require time and patience to collate.

For the Romano-British presence in northern and central Gaul in last years of the Western Roman Empire, the sources are two letters by Sidonius Apollinaris, Jordanes’ “Getica”, and the writings of Gregory of Tours and of Cassiodorus.

Sidonius was a Gallo-Roman bishop and senator who was contemporary with the events and a friend of the British leader he calls Riothamus, as well as being a friend of the Gallo-Roman official Arvandus who committed treason with King Euric of the Visigoths against Emperor Anthemius with whom Riothamus was allied.

According to the above sources, Riothamus sailed up the Loire with 12,000 men, established a base at Bourges, marched to Déols, was ambushed there by Euric, battled for hours, faced defeat, gathered as many men as he could and retreated into Burgundy. (The nearest ancient Burgundian town is Avallon, on elevated land protected by a tight river bend: see Google Maps.)