The Battle of the Margus or Battle of Margum was fought in July 285 for control of the Roman Empire between the armies of Diocletian and Carinus in the valley of the Margus River (today Great Morava) in Moesia (present day Serbia),[1][2] probably near the settlement of Margum.

[3][4] The battle proved to be the tipping point that led to the eventual resolution of the Crisis of the Third Century and the return of stability to the Empire.

Carinus had allegedly alienated men whose support his success depended upon, including mistreating the Senate and its womenfolk[clarification needed] and seducing the wives of his officers.

Some scholars suspect that Aristobulus was the officer responsible for the murder of Carinus, an argument that gains credibility in the fact that Diocletian afterward rewarded Aristobulus by confirming him in office as Praetorian Prefect and Consul for the remainder of 285.

[7] After his victory, Diocletian administered the oath of loyalty to Carinus' former troops, then turned his attention to the Danube frontier where the Marcomanni and Quadi were conducting raids across the border.