Battle of Adrianople (378)

The Battle of Adrianople was waged on August 9, 378 AD between the Roman army and Germanic tribes. Jealous of the military success of his counterpart and wanting a glorious victory for himself, the Emperor of the eastern part of the Roman empire, Valens, rushed to meet the Germans ahead of the Emperor of the western part of the Empire, Gratian. Already exhausted from forced marches, the battle began prematurely before the legions were deployed. The Visigoths along with Ostrogoths, Sarmatians, and Alans defeated the Romans and killed Valens, along with 40,000 Roman soldiers.

Adrianople was famous for being a battle where the Roman legions were defeated by a force consisting of almost entirely cavalry and produced a turning point in tactics where mounted forces gained prominence over infantry for the next 1000 years.