Marcus Maecilius Flavius Eparchius Avitus (c. 395 - 456, Western Roman Emperor (455 - 456). Made Magister militum (or Master of Soldiers) by the emperor Petronius Maximus, Avitus was sent on a diplomatic mission to his old student, Theodoric II king of the Visigoths, and was at Theodoric's court in Toulouse when Gaiseric invaded Rome, bringing Petronius Maximus's rule to a sudden end. Theodoric seized the opportunity and urged Avitus to assume the imperial throne, and with the acclamation of a gathering of Gallo-Roman senators, allowed himself to be persuaded. On July 9, 455, he was proclaimed emperor by the soldiers, and reached Rome that September.

The Italian populace never fully accepted his rule, so when his campaign against the Vandals failed in 456, and they pressed their blockade against Rome, his position became tenuous. Famine in Rome forced him to disband his Gothic bodyguard. But they needed to be paid, and he did not improve his standing with the Roman citizenry when he melted down a number of bronze statues to pay their outstanding wages. Ricimer and Majorian exploited this discontent by starting a general revolt.

Avitus fled to safety in Arles. A plea for help to Theodoric went unanswered, as the Gothic king was away in Spain campaigning against the Suevians. Avitus raised the best force he could and returned to Italy. He was defeated near Placentia, modern day Piacenza, and captured. His life was spared, and was allowed to become bishop of Placentia on October 17 or 18, 456; however, he still feared for his life and attempted to escape to safety in Gaul. He died on the way, by some accounts murdered.

His grandson was the poet Avitus of Vienne.