The Military Campaigns of Adrianople
James A. Arvites argues that the defeat of the Roman army at Adrianople in AD 378 changed the face of the Empire and led to the replacement of the infantry by heavy cavalry as the mainstay of its forces.
'These ever irreparable losses, so costly to the Roman state.' In those moving words Ammianus Marcellinus, contemporary soldier-historian, recorded his initial reaction to the Roman defeat by the Goths at Adrianople. On the morning of August 9th, 378, the Emperor Valens led the field army of the East from Adrianople in pursuit of the invading Barbarians, but by nightfall the Emperor and two-thirds of the Roman forces lay dead on the Thracian plain. The marauding Goths now stood unopposed in the Balkans. Adrianople, the worst defeat suffered by a Roman army since the Battle of Cannae during the Second Punic War, was the final episode in the long series of bloody and costly conflicts between Valens and the Goths.