In 392 AD, the Roman Empire was split into the Eastern and Western empires. Valentinian II led the west, while Theodosius I was in charge of the east. Both emperors favored Christianity over the old pagan gods, causing tension between the two rulers and members of the Senate. Although there was wide-spread violence on a small scale throughout the empire over the two main religions of the empire, for the most part the debate of Christianity versus Paganism was theological and academic. That all changed when Valentinian was found dead in his residence on May 15, 392. This is a category of roman empire coins.
Arbogast, a Frankish general, was the magister militum of the Western empire, making him the de facto ruler upon the death of Valentinian. He immediately sent word to Theodosius, saying the death was suicide. Flavia Galla, the wife of Theodosius I and sister of Valentianian II, convinced the emperor her brother’s death was murder, not suicide. The messages Arbogast was sending never made it past the Eastern praetorian prefect, Rufinus. Even though Arbogast’s uncle was chief commander of the Eastern army, he had few other friends in that part of the kingdom.
Expecting hostilities from the East, Arbogast took the prudent move of elevating the magister scrinii, Flavius Eugenius, to emperor on August 22. Eugenius was a native Roman and a respected scholar. The nomination was backed by the praetorian prefect of Italy, as well as many of the Roman senators who wanted to see a return to the pagan roots of the Empire. Eugenius appointed several pagan-friendly senators to important positions and restored the shrines of the Temple of Venus and Rome and the Altar of Victory. The actions garnered much criticism from the Bishop of Milan and was met with disfavor from Theodosius. Eugenius then removed all of the officials appointed by Theodosius in the West, when he gave that half of the empire to Valentinian, thusly eliminating all Eastern power in the area.
When a party of ambassadors arrived at the court of Theodosius from the West, the emperor committed to nothing but vague promises of acknowledging Eugenius as ruler. At what point Theodosius decided the West must be taken back is unclear, but he elevated his son, Honorius, who was only eight at the time, to emperor of the Western Empire in January of 393. Declaring Honorius as emperor was one thing – actually installing him in the West would be a different matter. The armies needed to be rebuilt and the task was left to the generals Stilicho and Timasius to bolster the ranks and get the troops battle-ready. One of Theodosius’s advisers, Eutropius, went from Constantinople to Lycopolis in Egypt, to consult with an old Christian monk about the invasion. The monk prophesized Theodosius would be victorious against Eugenius and Arbogast, but at great cost.
Theodosius led the invasion himself, leaving Constantinople in May, 394. His troops were complimented by forces from Syria, numerous barbarian auxiliaries and more than 20,000 Visigoths, including the chieftain, Alaric. The armies marched all the way to the Julian Alps unopposed. Arbogast had experience in military matters of this scale, having had to battle the usurper, Magnus Maximus, from Gaul. He decided his best chances were to leave the Alpine area undefended and to concentrate on Italy itself. His forces consisted of Franks, Gallo-Romans and Gothic auxiliaries.
Although the exact place of the battle is not yet known, the armies met at the River Frigidus, possibly near Vrhpolje, in the Vipava Valley of modern-day Slovenia. Other suggestions include an area somewhere between the settlements of Col and Sanabor, also in the same valley. Before the battle, the Western forces placed a status of Jupiter at the edge of the battlefield, as well as Hercules on their banners. The outcome of this battle would determine the fate of Christianity and Paganism within the Roman Empire and which religion would take root in the history of the Western World.
Theodosius attacked almost immediately upon encountering the opposing forces. He didn’t survey the field before engaging, resulting in heavy casualties and gaining little. Eugenius and Arbogast celebrated the first evening and sent a detachment of troops to flank Theodosius and trap him in the mountain passes. In the morning, Theodosius heard about the plot to surround him and charged once again. This time, the Western forces were now short on troops, since they were split trying to surround the pass. Along with the attack, Theodosius was fortunate to have the bora, strong winds that blow through the region, pummeling Eugenius with a headwind of dust. Arbogast’s lines broke in the attack and high winds, giving Theodosius the victory he was prophesized.
After the battle, Eugenius was brought to the camp of Theodosius and begged for mercy. He was beheaded and the Roman Empire was once again under the rule of a single emperor on September 6, 394 AD. Arbogast has fled, but committed suicide in the mountains after several days of wandering and realizing he had no means of escape.