Valentinian III (July 2, 419, Ravenna - March 16, 455, Rome), Western Roman Emperor (424 to 455). He was born as the only son of Constantius III and Galla Placidia, daughter of the emperor Theodosius. He was elevated as Caesar on October 23, 424 in Constantinople, and after a brief war in Italy, was installed as Emperor of the West in Rome on October 23, 425.

He was only six years of age when he received the title of Augustus, and during his minority the conduct of affairs was in the hands of first his mother, then after 433, Aetius. His reign is marked by the dismemberment of the Western Empire; the conquest of the province of Africa by the Vandals in 439; the final abandonment of Britain in 446; the loss of great portions of Spain and Gaul, in which the barbarians had established themselves; and the ravaging of Sicily and of the western coasts of the Mediterranean Sea by the fleets of Genseric.

As a set-off against these calamities there was the great victory of Aetius over Attila in 451 near Chalons, and his successful campaigns against the Visigoths in southern Gaul (426, 429, 436), and against various invaders on the Rhine and Danube (428-31).

The burden of taxation became more and more intolerable as the power of Rome decreased, and the loyalty of her remaining provinces was seriously impaired in consequence. Ravenna was Valentinian's usual residence; but he fled to Rome on the approach of Attila, who, after ravaging the north of Italy, died in the following year (453).

In 454 Aetius, between whose son and a daughter of the emperor a marriage had been arranged, was treacherously murdered by Valentinian. On March 16 of the following year, however, the emperor himself was assassinated by two of the barbarian followers of Aetius. He not merely lacked the ability to govern the empire in a time of crisis, but aggravated its dangers by his self-indulgence and vindictiveness.

Our chief original sources for the reign of Valentinian III are Prosper's Chronicles, Jordanes whose Gothic History was written in the 6th century, and the poet Sidonius Apollinaris. A modern secondary source is Oost, Galla Placidia Augusta (Chicago: University Press, 1968).