In 470 Euric defeated an attempted invasion of Gaul by the British king Riothamus and expanded his kingdom even further north, possibly as far as the Somme River, the March of Frankish territory.
Gregory of Tours seems to react to the outcome of the battle between the Goths and Britons: "Brittani de Bituricas a Gothis expulsi sunt, multis apud Dolesim vicum peremptis" (The Brittani were driven from Bourges by the Goths and many of them perished at the village of Déols).
It can probably be further narrowed to the period when Anthemius is known to have been organising a concerted effort to remove the Visigoths from Gaul between 468 and 471, a period during which an army led by the Briton Riothamus was defeated near Déols.
There, the ducks meet "King Arthur"—Artorius Riothamus, the last descendant of Lucius Artorius Castus, and find out that he is nowhere near the glorious benevolent ruler history has made him to be; instead, he's a common warlord without much morals to speak of.