Battle of the Frigidus

The Battle of the Frigidus, also called the Battle of the Frigid River, was fought between September 5–6 394, between the army of the Eastern Emperor Theodosius I and the army of Western Roman ruler Eugenius.

The defeat of Eugenius and his commander, the Frankish magister militum Arbogast, put the whole empire back in the hands of a single emperor. It would be nearly a century before another emperor would rule unilaterally, by which time (480) control of most of the west had become nominal at best. Most significantly, the battle was the last attempt to contest the Christianization of the empire; its outcome decided the outcome of Christianity in the western Empire.

Forebodings
In 313 Constantine I and Licinius I had legalized the Christian faith with the Edict of Milan. In Theodosius I had made the still young faith official religion of the State with the 380 Edict of Thessalonica. Conflict simmered between the Roman Senate, many of whom were not Christian, and the emperors in Constantinople and Milan who officially subscribed to Christian teachings. The senators wrote letters and argued for a return to traditional Roman beliefs, often stressing the protection and good fortune the old Roman gods had bestowed Rome since her beginnings as a small city-state. For their part, the Christian emperors emphasized the primacy of Christianity, although not all did so to the same extent. This clash between the Roman world's two main religions was for the most part merely an academic debate, without threats of armed uprisings, although small-scale violence was widespread.

On 15 May 392, however, the Western Emperor Valentinian II was found dead at his residence in Vienne, Gaul. Valentinian, who for a time showed some favoritism towards the Arians, had continued the imperial policy of suppressing the interests of adherents of the old pagan religions while supporting Christians. This policy had resulted in increasing tensions between the emperor and the senators.

When the Eastern Emperor Theodosius heard the news of Valentinian's death, Arbogast, who was the magister militum and de facto ruler of Western Empire, informed him that the young emperor had committed suicide.

Tensions between the two halves of the empire were heightened further that summer. Arbogast made several attempts to contact Theodosius, but apparently none got further than the ears of the Eastern praetorian prefect Rufinus. The responses that Arbogast received from Rufinus were unhelpful. Theodosius himself was slowly coming around to the belief that Valentinian had been murdered, in no small part because his wife Galla was convinced her brother's death was caused by treachery.

For his part, Arbogast had few friends in the Eastern court, although his uncle Richomeres was chief commander of the eastern cavalry. As it appeared increasingly likely that whatever course Theodosius decided upon would be hostile towards Arbogast, the Frank decided to make the first move.

On 22 August of that year, Arbogast elevated Flavius Eugenius, the Western imperial court's magister scrinii, to the purple. Eugenius was a well-respected scholar of rhetoric, and a native Roman, making him a far more acceptable candidate for the purple than the Frankish commander. His ascension was backed by the praetorian prefect of Italy, Nicomachus Flavianus the Elder, and also by many of the pagan members of the Roman Senate. However, some senators, notably Symmachus, were uneasy with this action.



After his elevation to emperor, Eugenius appointed several important pagan senators to key positions in the Western government. He also supported a movement to advance the traditional religion by granting it official recognition and by restoring important shrines such as the Altar of Victory and the Temple of Venus and Rome. These actions earned Eugenius withering criticism from Bishop Ambrose of Milan and did little to endear him to the Christian Theodosius.

As a Christian, Theodosius was distressed by the apparent pagan revival that was occurring under Eugenius's reign. In addition there was the issue of Valentinian's death, which had never been resolved to his satisfaction. Furthermore, Eugenius had removed all the high civil officers left by Theodosius when he had given the Western half of the empire to Valentinian, so that Theodosius had lost control of the Western Roman Empire.

When a party of Western ambassadors arrived in Constantinople to request that Eugenius be acknowledged as the Western augustus, Theodosius was noncommittal, even if he received them with presents and vague promises. Whether he had already decided on an offensive against Eugenius and Arbogast at this point is unclear. In the end, however, after declaring his son Honorius, then eight years old, as the western augustus in January of 393, Theodosius finally resolved to invade the West.

Campaign preparation
Over the following year and a half Theodosius marshalled his forces for the invasion. The Eastern armies had atrophied since the death of the emperor Valens and most of his soldiers at the Battle of Adrianople. It fell upon the generals Flavius Stilicho and Timasius both to restore discipline to the legions and to bring them back up to strength through recruitment and conscription.

At the same time another of Theodosius's advisers, the eunuch Eutropius, was sent out from Constantinople to seek the advice and wisdom of an aged Christian monk in the Egyptian town of Lycopolis. According to the accounts of the meeting given by Claudian and Sozomen, the old monk prophesied that Theodosius would achieve a costly but decisive victory over Eugenius and Arbogast.

The Eastern army set out towards the west from Constantinople in May 394. The re-galvanized legions were bolstered by numerous barbarian auxiliaries including over 20,000 Visigoth federates and additional forces from Syria. Theodosius himself led the army; among his commanders were his own generals Stilicho and Timasius, the Visigoth chieftain Alaric, and a Caucasian Iberian named Bacurios Hiberios.

Their advance through Pannonia until the Julian Alps was unopposed, and Theodosius and his officers must have had suspicions about what lay ahead when they discovered that the eastern ends of the mountain passes were undefended. Arbogast had, based on his experiences fighting against the usurper Magnus Maximus in Gaul, decided that the best strategy was to keep his forces united to defend Italy itself, and to that end he went so far as to leave the Alpine passes unguarded. Arbogast's forces consisted mainly of his fellow Franks and Gallo-Romans, plus his own Gothic auxiliaries.

Thanks to Arbogast's strategy of maintaining a single, relatively cohesive force, the Theodosian army passed unhindered through the Alps and descended towards the valley of the Frigidus River to the east of the Roman port of Aquileia. It was in this narrow, mountainous region that they came upon the Western army's encampment within the Claustra Alpium Iuliarum in a pass near present-day Vipava, Slovenia, in the first days of September.

The battle
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. 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, and the Georgian general Bacurius was among the dead.

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. 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.

Modern Interpretation
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.

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.

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 – within a generation the elite pagan families of Rome would give up any serious resistance to Christianity and re-invent themselves as the papal families of Late Antiquity.

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.