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 - Roman s , 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 .