Battle of the Frigidus - Wikipedia

On September 6, 394, the Battle of Frigidus occurred in Northern Italy between the forces of Eastern Roman Emperor Theodosius I who defeated those of Western Emperor Eugenius. From the article:

"The Battle
It is uncertain exactly where the battle took place. Though it has also been claimed that the location of the battle should be sought in the Upper Soča Valley, it has mostly been placed somewhere in the Vipava Valley. Whereas the Frigidus has been usually considered to be the Vipava River or Hubelj Creek and the battle to take place near Vrhpolje, recent research suggests that it actually took place some kilometers away, between Col and Sanabor.[3]

Before the battle, Eugenius and Arbogast placed a statue of Jupiter on the edge of the battlefield, and had applied images of Hercules on the army banners.[4] This way they hoped to repeat the victories of Rome in earlier days, when it had always relied on the old gods for support in battle. On the first day of battle the old gods seemed to be winning. Theodosius attacked almost immediately, having undertaken little to no prior reconnaissance of the field of battle. He committed his Gothic allies to action first, perhaps hoping to thin their ranks through attrition and lessen their potential threat to the Empire. The Eastern army's headlong attack resulted in heavy casualties but little gain: 10,000 of the Gothic auxiliaries are reported to have been slain, and the Georgian general Bacurius was among the dead.[5]

Day's end saw Eugenius celebrating his troops' successful defense of their position while Arbogast sent out detachments to close off the mountain passes behind Theodosius's forces.

After a sleepless night, Theodosius was cheered by the news that the men Arbogast had sent to bottle him up in the valley intended to desert to his side. Buoyed by this favorable development, Theodosius' men attacked once again. This time nature was on their side as a fierce tempest—apparently the bora, a regular occurrence in the region—blew along the valley from the east. Other stories tell of Theodosius praying to God for a storm, which God subsequently granted.[6]

The high winds blew clouds of dust into the faces of the Western troops (legend also says that the fierce winds even blew the Western troops' own arrows back at them). Buffeted by the winds, Arbogast's lines broke and Theodosius gained the decisive victory that the Egyptian monk had prophesied.

In the aftermath, Eugenius was captured and brought before the emperor. His pleas for mercy went unanswered and he was beheaded. Arbogast escaped the defeat and fled into the mountains, but after a few days' wandering, he concluded escape was impossible and committed suicide.

Religious character of the conflict
While the version of the battle in which a divine wind defeated the pagan enemies of Theodosius became popular in late antiquity, modern historians, most notably Alan Cameron, have disputed the reliability of this version of events. Cameron asserts that the idea that Eugenius and Arbogastes were pagans or supporters of pagans was created to justify Theodosius' campaign against them, and that other usurpers, such as Magnentius, were falsely branded as pagans after their defeat. The idea that Theodosius' enemies were pagans originates in the church historian Rufinus, and only the sources dependent on Rufinus mention this idea.[7]

In addition, the earliest source to mention the decisive bora wind was Ambrose of Milan, but he states in his sermon on Psalm 36 that the wind blew before that battle, and demoralized Theodosius' enemy before any fighting began. This idea was probably picked up by the poet Claudian, who, in his fanciful and propagandistic poetry for the Theodosian family, moved the wind to the decisive moment of the battle. Claudian seems to have been making a classicizing allusion to Silius Italicus, whose account of the Battle of Cannae mentioned a similar wind blowing spears and weapons back. From Claudian's poetry, which was popular in both eastern and western halves of the Roman Empire, the idea of the bora wind deciding the battle spread. It fit well with the other idea that the battle was one between pagans and Christians: Theodosius, as the Christian emperor, was aided by God in the form of the wind.[8]

Aftermath
It had been a costly but total victory for Theodosius, and a total loss for Eugenius. The western provinces quickly submitted to Theodosius. A mere four months later he died, leaving the government in the hands of his young children Honorius and Arcadius.

Most significantly, the battle has often been seen as the last attempt to contest the Christianization of the empire. According to Rufinus, the battle is on a par with the Battle of the Milvian Bridge in importance, for it was seen not only as a victory in a civil war, but a vindication of the Christian God and the triumph of Christianity[9] – within a generation the elite pagan families of Rome would give up any serious resistance to Christianity.[10]

However, the battle also accelerated the collapse of the Roman army in the west. The legions were already losing their effectiveness, due to reorganizations and a decline in the quality of their training and discipline. The losses at the Battle of the Frigidus weakened the western legions. This downturn in the capabilities of the Roman soldiers meant an increasing reliance by the Empire on barbarian mercenaries employed as foederati, who often proved to be unreliable, or even treacherous."