Nic Fields draws on detailed knowledge of available sources and his own visits to the battlefield to set the battle within the context of its political situation and religious impact upon history. The Battle of the Frigidus River, fought on 5 and 6 September 394 in what is now Slovenia, was a crucial clash between the Eastern Roman emperor, Theodosius (later ‘the Great’), and the usurper Eugenius, who had seized power in the Western Empire. The battle was hard fought and lasted two days. At the end of the first, Theodosius was on the brink of defeat but the following day a great wind blowing against his enemy resulted in him securing a decisive victory. Eugenius, like Theodosius, was a Christian but, unlike Theodosius, he was tolerant of pagans, so this wind was seen as miraculous and the victory was attributed to God’s favour. Nic Fields’ narrative sets the battle in the context of the political situation within the empire and the campaigns leading up to this pivotal showdown. The armies of both protagonists are described, the tactics and strategy of the time discussed. Drawing on his detailed knowledge of the sources, the latest research and his own visits to the battlefield and surrounding terrain, the author then recounts the battle itself. Importantly he reveals the natural phenomenon behind the ‘miracle’ that saved Theodosius. Finally, the author analyzes and assesses the aftermath and consequences of this significant clash, which included Eugenius’ execution and the temporary reunification of the Eastern and Western Roman empires.