In 851, Frankish garrisons left in the previous year in Rennes and Nantes capitulated to Nominoë, who raided eastwards, ravaging Le Mans.
His successor, his son Erispoe, took command of the Breton force and continued its offensive in alliance with Lambert II of Nantes, a renegade Frank dispossessed by Charles the Bald.
[2] Faced with the threat, Charles sought the support of his brother Louis the German, obtaining a contingent of Saxons to increase the size of his force.
Rather than engage in a melée, the Bretons harassed the heavily armed Franks from a distance, in a manner comparable to Parthian tactics, but with javelins rather than archers.
After two days of this sort of fighting, Frankish losses in men and horses were mounting to catastrophic levels, while the Bretons suffered few casualties.
According to the Annals of Saint-Bertin "Erispoe, son of Nominoë from Charles, in the City of Angers submitted and received a gift of symbols of the monarchy that came from his father, adding also Rennais, Nantais and Retz.