Valentinian II (; 37115 May 392) was a Roman emperor in the western part of the Roman Empire between AD 375 and 392. He was at first junior co-ruler of his half-brother, then was sidelined by a usurper, and finally became sole ruler after 388, albeit with limited de facto powers. He was the youngest emperor (co-ruler) in the Western Roman Empire (aged 4).
A son of emperor Valentinian I and empress Justina, he was raised to the imperial office at the age of four by military commanders upon his father's death. Until 383, Valentinian II remained a junior partner to his older half-brother Gratian in ruling the Western empire, while the East was governed by his uncle Valens until 378 and Theodosius I from 379. When the usurper emperor Magnus Maximus killed Gratian in 383, the court of Valentinian II in Milan became the locus of confrontations between adherents to Nicene and Arian Christianity. In 387, Maximus invaded Italy, spurring Valentinian II and his family to escape to Thessalonica where they successfully sought Theodosius's aid. Theodosius defeated Maximus in battle and re-installed Valentinian II.
Valentinian II ruled from Gaul after being restored to power in 388. He was largely under the control of Arbogast, a powerful general and regent. In 392, Valentinian II was found dead in his palace, a death some at the time believed was a suicide and others a murder orchestrated by Arbogast, whom the emperor had tried to dismiss.
Early life and accession (371–375)
He was born Valentinianus to Emperor Valentinian I and his second wife Justina. His paternal half-brother Gratian had been sharing the imperial title with their father since 367. He had three sisters: Galla, Grata, and Justa.
The elder Valentinian died on campaign in Pannonia in 375. Neither Gratian (then in Trier) nor his uncle Valens (emperor of the East) were consulted by the army commanders on the scene. The four-year-old Valentinianus and his mother Justina were living in Sirmium or an imperial villa near Carnuntum.
Valentinian I's leading generals and officials did not acknowledge Gratian as his father's successor. These officials—among them Merobaudes, Petronius Probus, Equitius and Cerealis (Valentinianus's maternal uncle), instead had the four-year-old Valentinianus brought to Aquincum where they named him augustus Valentinian II on 22 November 375.
The army and its Frankish general Merobaudes were likely concerned about Gratian's limited military skills and—to prevent a split within its ranks—elevated the four-year-old to emperor, with the generals assuming that they themselves would take command.
Merobaudes may have also wanted to prevent rivals such as Sebastianus and Count Theodosius (not to be confused with Emperor Theodosius I) from becoming emperor or gaining independent power; within a year of Valentinian's elevation, Sebastianus was removed to a distant posting and Count Theodosius was executed.
Reign from Milan (375–387)
thumb|upright|left|Solidus of Valentinian II
Gratian was forced to accommodate the generals who supported his half-brother; he purportedly enjoyed seeing to Valentinian's education. According to Zosimus, Gratian governed the trans-alpine provinces including Gaul, Hispania, and Britain; Valentinian was nominally ruler of Italy (part of Illyricum) and North Africa. In fact, however, Gratian governed the whole Western empire; Valentinian was marginalized and did not issue any laws. In 378 their uncle Emperor Valens was killed by the Goths in Adrianople; Gratian invited the general Theodosius to be emperor in the East. As a child, Valentinian II was under the pro-Arian influence of his mother the empress Justina and of the courtiers at Milan. Such influence was opposed by the Nicene bishop of Milan, Ambrose. he admitted he was not the cause of the decision to remove the altar in the first place.
In 385 Ambrose refused an imperial order to hand over the Portian Basilica (now the Basilica of San Vittore al Corpo) for the celebration of Easter by the Imperial court. His refusal angered not just Valentinian but also Justina, high-ranking officials, and court Arians including Goths. Ambrose argued in his letter that Justina influenced her young son to oppose the Nicean party championed by Ambrose, and framed her motivation as purely selfish.
But the wider imperial court also opposed Ambrose's claim, and the praetorian prefect and the emperor's counsellors demanded that he turn over the basilica. To this end, he wrote a scathing missive attacking Valentinian for plotting against God.
In 386 to 387, Maximus crossed the Alps into the Po valley to threaten Milan. Valentinian II and Justina fled to Emperor Theodosius I 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. On the Eastern emperor's coinage, Valentinian continued to be represented with the "unbroken" legend like Arcadius, depicting both of them as Theodosius' junior colleagues. <blockquote> While events of various sorts were taking place in the East throughout Thrace, the public order was disturbed in Gaul. Valentinian the emperor was shut up in Vienne in the palace, and reduced almost below the position of a private person, and the military command was given over to the Frankish allies, and even the civil offices fell under the control of Arbogast's faction, and no one of all the oathbound soldiery was found to dare to heed the familiar speech or obey the command of the emperor.</blockquote>
Arbogast once refused to allow Valentinian to lead a military expedition against barbarian invaders that were threatening Italy. His domination over the emperor was to the point where, in a report that Mark Hebblewhite characterized as "admittedly outlandish"; the general is described as murdering Harmonius, a friend of Valentinian suspected of taking bribes, in the emperor's presence. Valentinian wrote to Theodosius and Ambrose complaining of his subordination to his general. It is ambiguous on the question of the emperor's death, which is not surprising, as Ambrose represents him as a model of Christian virtue. Suicide, not murder, would make the bishop dissemble on this key question.
The young man's body was conveyed in ceremony to Milan for burial by Ambrose, mourned by his sisters Justa and Grata. He was laid in a porphyry sarcophagus next to his brother Gratian, most probably in the Chapel of Sant'Aquilino attached to San Lorenzo. He was deified with the .
At first Arbogast recognized Theodosius's son Arcadius as emperor in the West, seemingly surprised by his charge's death. After three months, during which he had no communication from Theodosius, Arbogast selected an imperial official, Eugenius, as emperor. Theodosius initially tolerated this regime but, in January 393, elevated the eight-year-old Honorius as augustus to succeed Valentinian II. Civil war ensued and, in 394, Theodosius defeated Eugenius and Arbogast at the Battle of the Frigidus.