Valentinian II (371 – 15 May 392), was a Roman Emperor from 375 to 392.

Flavius Valentinianus was born to Emperor Valentinian I and his second wife, Justina. He was the half-brother of Valentinian’s other son, Gratian, who had shared the imperial dignity with his father since 367. The elder Valentinian died on campaign in 375. Instead of merely acknowledging Gratian as his father’s successor, Valentinian I’s generals acclaimed the four-year old boy augustus on 22 November 375. The army may have been uneasy about Gratian's lack of military ability, and so raised a boy who would not immediately aspire to military command.

Gratian, forced to accommodate the generals who supported his half-brother, governed the trans-alpine provinces (including Gaul, Hispania, and Britain), while Italy, part of Illyricum, and Africa were under the rule of Valentinian. In 378 their uncle, the Emperor Valens, was killed in battle with the Goths at Adrianople, and Gratian invited the general Theodosius to be emperor in the East. As a child, Valentinian II was under the influence of his Arian mother, the Empress Justina, and the imperial court at Milan, an influence contested by the Catholic bishop of Milan, Ambrose.

Justina used her influence over her young son to oppose the Catholic party which was championed by Ambrose. In 386 she sanctioned the requisitioning of a Milanese church for Arian usage. Ambrose and his congregation barricaded themselves inside the church, and the imperial order was rescinded. Magnus Maximus used the emperor’s heterodoxy against him, and even his eventual protector, Theodosius, cast aspersions on his Arianism. Valentinian also tried to restrain the despoiling of pagan temples in Rome. Buoyed by this instruction, the pagan senators, led by Aurelius Symmachus, the Prefect of Rome, petitioned in 384 for the restoration of the Altar of Victory in the Senate House, which had been removed by Gratian in 382. Valentinian, at the insistence of Ambrose, refused the request and, in so doing, rejected the traditions and rituals of pagan Rome to which Symmachus had appealed.

In 383 Magnus Maximus, commander of the armies in Britain, declared himself Emperor and established himself in Gaul and Hispania. Gratian was killed in Gaul fleeing him. Although Maximus demanded that Valentinian submit to him at his capital of Trier, the government at Milan, through the mediation of Ambrose, managed a temporary accommodation with the usurper, and Theodosius recognized Maximus as co-emperor of the West. However, in 387 Maximus crossed the Alps into the Po valley and threatened Milan. Valentinian II and Justina fled to Theodosius in Thessalonica. The latter came to an agreement, cemented by his marriage to Valentinian’s sister Galla, to restore the young emperor in the West. In 388 Theodosius marched west and defeated Maximus. Valentinian’s court was ensconsed at Vienne in Gaul, watched over by the Frankish general Arbogast, who was appointed magister militum. Although Theodosius raised both his sons to the imperial purple during Valentinian's lifetime (Arcadius in 383, Honorius in 392), he never moved to supplant Valentinian as a legitimate emperor.

On 15 May 392, Valentinian was found hanged in his residence in Vienne. Arbogast maintained that it was suicide. However, Valentinian had complained to Theodosius about Arbogast’s control over him. Thus when word of his death reached Constantinople, Theodosius believed, or at least suspected, that Arbogast had engineered Valentinian's demise. These suspicions were further fueled by Arbogast's elevation of Eugenius, a pagan official, to the position of Western Emperor, and the veiled accusations made by Ambrose during his funeral oration for Valentinian.

Valentinian II's death sparked a civil war between Eugenius and Theodosius over the rulership of the West. Theodosius’ victory in 394 led to the final brief reunification of the Roman Empire before the ultimate irreparable division of the empire under his sons.

Valentinian himself seems to have exercised no real authority, and was a figurehead for various powerful interests: his mother, his co-emperors, and powerful generals. Since the Crisis of the Third Century, the empire had been ruled by powerful generals, a situation formalised by Diocletian and his collegiate system. While Constantine and his sons had been strong military figures, they had also re-established the practice of hereditary succession, adopted by Valentinian I. The obvious flaw in these two competing requirements came in the reign of Valentinian II, a child. His reign was a harbinger of the fifth century, when children or nonentities, reigning as emperors, were controlled by powerful generals and officials.

* Stephen Williams & Gerard Friell, Theodosius: the Empire at Bay. (Routledge, 1994)

* De Imperatoribus Romanis on Valentinian II

*De Imperatoribus Romanis on Eugenius and Arbogast