Roman army of the mid-Republic placed unprecedented strains on Roman manpower, not least on the Order of Knights and the First Class of commoners which provided the cavalry. During Hannibal's apocalyptic march through Italy (218–216 BC), thousands of Roman cavalrymen were killed in the field. The losses were especially serious for the equestrian order, which also provided the army's senior officers. Livy relates how, after Cannae, gold rings (a badge of knightly rank), recovered from the corpses of Roman knights formed a pile one "modius" (about 9 litres) large. In the succeeding years 214–203 BC, the Romans kept at least 21 legions in the field
Early Middle Ages had broken down, and the Roman army comprised mainly barbarians and soldiers recruited for a single campaign. The general decline in discipline also led to the use of smaller shields and lighter weaponry. Not wanting to share the glory, Eastern Emperor Valens ordered an attack on the Therving infantry under Fritigern without waiting for Western Emperor Gratian, who was on the way with reinforcements. While the Romans were fully engaged, the Greuthung cavalry arrived. Only one-third of the Roman army managed to escape. This represented the most shattering defeat that the Romans had suffered since the Battle of Cannae (216