On this day in 378AD two Roman field armies under the emperor Valens were demolished at the battle of Adrianople by uppity Goths. The emperor himself was killed and two thirds of some of the empire's best troops were wiped out. It was a disaster like Rome hadn't seen since Teutoburger Wald in 9AD. The Roman army was never the same.
Thirty-two years later, the Visigoths under Alaric would sack the Eternal City itself.