Flavius Eugenius (died 6 September 394) was a usurper in the Western Roman Empire (392–394) against Emperor Theodosius I.
Though himself a Christian, he was the last Emperor to support Roman polytheism.
A former teacher of grammar and rhetoric, as well as magister scrinorum, Eugenius was an acquaintance of the Frank
magister militum and of the de facto ruler of the Western Roman Empire, Arbogast.
Rise to power -
Following the death of Valentinian II, Arbogast, who had probably been the cause of Valentinian II's murder or suicide,
elevated Eugenius to the purple (22 August 392). The choice of Eugenius, over proclaiming himself, offered to Arbogast two
strong advantages: first, Eugenius, a Roman, was more suitable than Arbogast, a Frank, as an emperor; furthermore, the
Roman Senate would have been more likely to have supported Eugenius than Arbogast.
Civil, religious, and military policies -
After being installed as Emperor, Eugenius changed the imperial administrators. When Theodosius had left the western half
of the empire to Valentinian II, he had put his own men in the highest civil offices, to keep a strong grasp on the whole
empire. Eugenius replaced these administrators with others loyal to himself, coming from the senatorial class. Virius
Nicomachus Flavianus the Elder became Praetorian Prefect of Italy, his son Nicomachus Flavianus the Younger received the
title of Prefect of Rome, while the new praefectus annonae was Numerius Proiectus.
Eugenius was nominally a Christian, and therefore was reluctant to accept a program of imperial support to Polytheism. His
men, however, convinced Eugenius to use public money to fund 'Pagan' projects, such as the rededication of the Temple of
Venus and Rome and the restoration of the Altar of Victory within the Curia (removed by Emperor Gratian). This religious
policy created tension with Theodosius and the powerful and influential Bishop Ambrose, who left his see in Milan when the
imperial court of Eugenius arrived.
Eugenius was also successful in the military field, notably in the renovation of old alliances with Alamanni and Franks.
Arbogast, who was Frank and had also Alamanni and Frank soldiers in his ranks, marched to the Rhine frontier, where he
impressed and pacified the Germanic tribes by parading his army in front of them.
When he was elected emperor, Eugenius sent ambassadors to Theodosius's court, asking for recognition of his election.
Theodosius received them, but started to gather troops to defeat Eugenius. Theodosius also promoted his eight-year-old son
Honorius to the rank of "Augustus" of the West in January 393.
Theodosius then moved from Constantinople with his army, and met Eugenius and Arbogast in the Battle of the Frigidus (on
the modern Italy-Slovenia border) on 6 September 394. The bloody battle lasted two days, and was marked by unusual
astronomical and meteorological events, but in the end Theodosius won. Arbogast immediately committed suicide after the
defeat, while Eugenius was held for execution as a criminal, his head afterward being displayed in Theodosius' camp.
The reign of Eugenius marked the end of an era and the beginning of a new one. A year later Theodosius died, dividing his
empire between his two sons. This had happened many times before in the previous two centuries, but this time it was to be
final - the Roman Empire never reunited even under Leo I the Thracian, and soon after his reign, the western half fell.
Eugenius also represented the last opportunity for the Pagans, with the senatorial class, to oppose the Christianization
of the Empire. The Battle of the Frigidus was part of a trend towards using increasing percentages of barbarian troops,
especially in the west, where it led to the weakening of the empire itself.