"God instantly answered him" ~ The victory of Theodosius the Great at the Battle of the River Frigidus

A silver miliarnse of Eugenius, showing Gloria Romanorum -- "Glory of the
Romans" on the reverse side.

This day, September 6, is the anniversary of the climax of the Battle of the Frigidus River where the Roman Emperor Theodosius the Great and his barbarian allies defeated the western puppet-emperor Eugenius and the Frankish generalissimo Arbogast. You’ve probably never heard of this battle, but had its outcome been different, the course of Western civilization would have been quite different. This was the last battle in which traditional Roman paganism sought to defeat and overcome Christianity, but in the effort, was itself crushed forever.

The exact location of the battle is not known, but the Frigidus River is today called the Vipava and runs through present-day Slovenia. Writing about 40 years after the event, the ancient historian Sozomen describes the political situation which led to the battle:

A certain man named Eugenius, who was by no means sincere in his professions of Christianity, aspired to sovereignty, and assumed the symbols of imperial power. He was hoping to succeed in the attempt safely, for he was led by the predictions of individuals who professed to foresee the future by the examination of the entrails and livers of animals and the course of the stars. Men of the highest rank among the Romans were addicted to these superstitions. Flavian, then a prætorian prefect, a learned man, and one who appeared to have an aptitude for politics, was noted for being conversant with every means of foretelling the future. He persuaded Eugenius to take up arms by assuring him that he was destined for the throne, that his warlike undertakings would be crowned with victory, and that the Christian religion would be abolished.

Deceived by these flattering representations, Eugenius raised an army and took possession of the gates into Italy, as the Romans call the Julian Alps, an elevated and precipitous range of mountains. These he seized beforehand and fortified, for they had but one path in the narrows, and were shut in on each side by precipices and the loftiest mountains.

Not to be outdone, Theodosius consulted a sooth-sayer of his own, a certain monk from Egypt named John, who predicted that “the war would terminate in favor of Theodosius, and that the tyrant would be slain, but that, after the victory, Theodosius himself would die in Italy.”

What Sozomen does not relate here is that Eugenius was little more than the puppet of Arbogast, the powerful Frankish general who had previously served as magister militum in praesentalis of Valentinian II, the Western emperor. After the suspicious suicide of Valentinian II, Arbogast named Eugenius as emperor. The irregularities of this situation, coupled with the re-establishment of pagan temples throughout the West, soon brought matters to a crisis that required a military solution. Sozomen continues:

[Theodosius] proceeded towards Italy, crossed the Alps and took the first guard-posts. On descending from the heights of these mountains, he perceived a plain before him covered with infantry and cavalry, and became at the same time aware that some of the enemy's troops were lying in ambush behind him among the recesses of the mountains. The advance guard of his army attacked the infantry stationed in the plain, and a desperate and very doubtful conflict ensued. Further, when the army surrounded him, he considered that he had come into the power of men, and could not be saved even by those who would desire to do so, since those who had been posted in his rear were seizing the heights.

The first day of the battle had been nearly catastrophic for Theodosius. According to the New History of Zosimus written about a century after the fact, “the greater part of the allies of Theodosius were slain, with their commander Bacurius, who fought very courageously at their head, while the other commanders escaped very narrowly with the remainder.” Stymied and surrounded by the forces of Eugenius and Arbogast, Theodosius began to despair and sought a divine solution to what would almost certainly be an ignominious defeat the next day. God’s response, however, was not long in coming. Sozomen continues:

He fell prone upon the earth, and prayed with tears, and God instantly answered him. For the officers of the troops stationed in ambush on the height sent to offer him their services as his allies, provided that he would assign them honorable posts in his army. As he had neither paper nor ink within reach, he took up some tablets, and wrote on them the high and befitting appointments he would confer upon them, provided that they would fulfill their promise to him. Under these conditions they advanced to the emperor.

The issue did not yet incline to either side, but the battle was still evenly balanced in the plain, when a tremendous wind descended into the face of the enemy. It was such an one as we have never before recorded, and broke up the ranks of the enemies. The arrows and darts which were sent against the Romans, as if projected by the opposing ranks, were turned upon the bodies of those who had cast them, and their shields were wrenched from their hands and whirled against them with filth and dust. Standing thus exposed in a defenseless condition to the weapons of the Romans, many of them perished while the few who attempted to effect an escape were soon captured.

Eugenius threw himself at the feet of the emperor, and implored him to spare his life. But while in the act of offering up these entreaties, a soldier struck off his head. Arbogastes fled after the battle and fell by his own hands.

A gold solidus of Theodosius I showing the victorious emperor and a bound captive
on the reverse.

Though Frigidus River was a great victory for Theodosius, the battle had pitted the dwindling Imperial armies against each other resulting in heavy losses of veteran Roman soldiers which could not easily be replaced. The result of these losses was an acute manpower shortage that would afflict the empire, especially in the West, and render it largely helpless in the face of large-scale barbarian invasions over the next 20 years.

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As for Theodosius himself, the Battle of Frigidus River allowed him to unify the Roman Empire under a single emperor for what would be the last time. He would descend into Italy and there face the wrath of Saint Ambrose in Milan who excommunicated the emperor for massacring 30,000 citizens in Thessalonika while proceeding from Constantinople to make war in the West. Theodosius would famously repent, but died a little while later in Milan, as predicted by the monk John before the battle.

Read more about these fascinating historical figures in the Ecclesiastical History by Hermias Sozomen.