Saint-Maur-des-Fossés owes its name to an abbey founded in 638 by Queen Nanthild, regent for her son Clovis II, at a place called "Fossati" in Medieval Latin, "Les Fossés" in modern French, meaning "the moats". This place, located at the narrow entrance of a loop where the Marne River made its way round a rocky outcrop, was probably named after the moats of an ancient Celtic oppidum and later a Roman castrum; the site was known in medieval documents as "Castrum Bagaudarum", at a time when the marauding Bagaudae had developed a legendary reputation as defenders of Christians again Roman persecution. Massive foundations, sited so far from a "Roman frontier", were attributed by C. Jullian to a temple or a villa instead. In Merovingian times, Gallo-Roman villas in the royal fisc were repeatedly donated as sites for monasteries under royal patronage.