He had little time to enjoy his position or to learn anything from its opportunities because the legions of Syria revolted and declared Elagabalus ruler of the Roman Empire. When Macrinus was defeated on June 8, 218, at Antioch, Diadumenian followed his father's death. According to the Scriptores Historiae Augustae, Diadumenian emulated Macrinus in tyranny. He called upon his father not to spare any who might oppose them or who made plots. His head was cut off and presented to Elagabalus as a trophy.