The Visigothic kings of Toulouse, one of the "foederati" (allies) of the Roman Empire in the West and limited to Aquitania and Toulouse, soon began encroaching on neighboring territories. As Roman allies the Visigoths helped defeat Germanic invaders in Spain (notably the Suebi), taking advantage of their position to expand their territory south of the Pyrenees. They tried to conquer the Mediterranean coast of the province of Gallia Narbonensis, but were opposed by Rome. In 439 the Roman general Litorius defeated the Visigoths at Narbonne, driving them back to Toulouse. Although he besieged the city, he was defeated and taken prisoner. Avitus, the praetorian prefect of Gaul with influence on King Theodoric I of the Visigoths, was then sent to Toulouse and concluded a peace. In 451, threatened by an invasion of the Huns in Gaul, he negotiated a treaty between Rome and the Visigoths and they defeated the Huns. In 455 Avitus, "magister militum" (senior military officer of the Empire) on a diplomatic mission to King Theodoric II of the Visigoths, was proclaimed the new Roman emperor in Toulouse by his Visigothic friends amid news that the Vandals had sacked Rome and Emperor Petronius Maximus had been murdered. Avitus' reign in Rome was brief, and he was defeated by his enemies in 456. This antagonized the Visigoths, who warred with the new Roman leaders, and a weaker Rome gave way. The Narbonne region was conquered by the Visigoths in 462.