Battle of the Frigidus River

The Battle of the Frigidus, also called the Battle of the Frigid River, was fought on 5 and 6 September 394 between the armies of the Roman emperor Theodosius the Great and the rebel augustus Eugenius, in the eastern border of Roman Italy.^¹ Theodosius won the battle and defeated the usurpation of Eugenius and Arbogast, restoring unity to the Roman Empire.^¹ The battlefield, in the Claustra Alpium Iuliarum near the Julian Alps through which Theodosius's army had passed, was probably in the Vipava Valley – with the Frigidus River being the modern Vipava – or possibly in the valley of the Isonzo.^¹