Born of a distinguished Gallic family, Avitus was a son-in-law of the Christian writer Sidonius Apollinaris. By taking advantage of his great influence with the Visigoths who were settled at Toulouse, Avitus was able in 451 to persuade their king, Theodoric I, to join the Roman general Aetius in repelling the invasion of Gaul by the Huns under Attila. Avitus was appointed magister utriusque militiae ("master of both services") by the Western emperor Petronius Maximus (reigned 455). When Maximus was killed, the Goths proclaimed Avitus emperor at Toulouse, and this claim was upheld by the Gallo-Romans at Arles. The new emperor proceeded to Rome but was forced by the general Ricimer to abdicate (Oct. 17, 456) and to become bishop of Placentia. [Encyclopaedia Britannica CD '97]
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"The next emperor was proclaimed not in Italy but in Gaul. This was Avitus, the friend and nominee of the Visigothic king Theoderic II, who was proclaimed emperor in July 455 at Tolosa (modern Toulouse), where Theoderic had established his court. The following year, however, the Suevian army commander Ricimer rebelled at Ravenna. Avitus marched against him but was captured in battle at Placentia (modern Piacenza) in October 456. Ricimer neutralized him by making him bishop of Placentia, but Avitus was soon forced to flee back to Gaul and died shortly afterwards. Avitus's overthrow and murder was followed by an 18-month interregnum while Ricimer made futile attempts to win recognition for his chosen successor Majorian from the eastern emperor Leo I (457-474)." [Chris Scarre, Chronicle of the Roman Emperors, Thames and Hudson Ltd., London, 1995]