How did the Visigoths expand their power in Gaul after Roman rule weakened?

The Visigoths expanded their power in Gaul by initially operating as foederati (federated allies) of the Roman Empire, a status granted in 418 when they were settled in the province of Aquitania Secunda. While serving as allies, they persistently sought to extend their territory at the expense of the weakening Western Empire.12

The transition to an independent power occurred under King Euric (466–484), who declared himself an independent monarch in 475. During his reign, the Visigothic kingdom, centered at Toulouse, reached its greatest extent, stretching from the Loire River to the Pyrenees and the Rhône River, while also incorporating much of Spain.12

This dominance in Gaul was significantly curtailed in 507, when the Franks led by Clovis I defeated and killed King Alaric II at the battle of Vouillé. Following this defeat, the Visigoths lost most of their Gallic possessions, retaining only Septimania along the Mediterranean coast.12