Numerian headed with his army for Rome, where a triumph was awaiting him, leaving the Persians astonished by the inexplicable retirement of a victorious army. However, Numerian's health was broken by the climate, and being unable to bear the heat of the sun, was borne on the march in a covered litter. Arrius Aper, the Praetorian prefect, assumed the conduct of affairs in his name, but his ambitious temper excited the suspicion of the troops. At Heraclea in Thrace they broke into the Imperial tent, and Numerian was found dead. Diocletian, commander of the body-guards, affirmed that Numerian had been assassinated by the praefect, and after executing the latter he was proclaimed emperor by the soldiers.