Battle of Adrianople (378)

The second Battle of Adrianople (August 9, 378) was fought between a Roman army led by the Emperor Valens and Germanic tribes (mainly Visigoths and Ostrogoths) commanded by Fritigern. The battle took place at today's Edirne (Turkey) and ended with an overwhelming victory of Germanic tribes. Emperor Valens, who is accused of causing the defeat by failing to wait for reinforcements, and was among 40,000 Roman soldiers lost on the battlefield. It was one of the major victories of so-called barbarians over the Roman forces, which aided several Germanic tribes to gain rights of accommodation within the Balkan territories and intrude into the Roman Empire. Ongoing Germanic intrusions resulted in the division of the Empire into two halves on 395 AD and to the extinction of the Western half in 476 AD.

It was the first set battle that the Romans had ever lost. As such, this date can be taken as a convenient dividing point between the ancient world and the middle ages.