Which Roman emperor defeated the usurper Avidius Cassius in 175 CE without a battle?

Marcus Aurelius defeated the usurper Avidius Cassius in 175 CE without a battle.

Avidius Cassius, a successful Roman general in the eastern provinces, proclaimed himself emperor after hearing a false report that Marcus Aurelius had died. Cassius gained support in Egypt and parts of Syria, but his revolt lasted only about three months.

Marcus Aurelius moved east with an army, yet the confrontation never became a full-scale civil war. Cassius was murdered by two of his own officers near Antioch, and his head was sent to Marcus. The emperor reportedly refused to celebrate the killing and treated Cassius’s family with relative clemency.

The episode illustrates both the danger of distant military commanders and the importance of reliable imperial communications. It is sometimes confused with the later civil wars involving Marcus Aurelius’s son Commodus, who succeeded him in 180 CE.