[W]ithin a generation, the Roman order was shaken to its core and Roman armies, as one contemporary put it, 'vanished like shadows'. In 376, a large band of Gothic refugees arrived at the Empire's Danube frontier, asking for asylum. In a complete break with established Roman policy, they were allowed in, unsubdued. They revolted, and within two years had defeated and killed the emperor Valens - the one who had received them - along with two-thirds of his army[.]