In 451, Gondioc joined forces with Flavius Aetius against Attila, the king of the Huns, on the Catalaunian Plains. In 457, he quelled a rebellion in Lyons and took over the city in breach of the terms of his relationship with the Romans. In response, Emperor Majorian expelled Gundioc from the city. After Majorian's assassination in 461, Gondioc resumed an expansionist policy. He made Lyons his new capital, taking possession of the provinces of Gallia Lugdunensis (now Burgundy) and, in 463, Gallia Viennensis (Rhône valley).