 In 217 , the emperor Caracalla was assassinated and replaced by his Praetorian prefect , Marcus <unk> Macrinus . Caracalla 's maternal aunt , Julia Maesa , successfully instigated a revolt among the Legio III Gallica to have her eldest grandson ( and Caracalla 's cousin ) , Elagabalus , declared emperor in his place . Macrinus was defeated on 8 June 218 at the Battle of Antioch . Elagabalus , barely fourteen years old , became emperor , initiating a reign remembered mainly for sex scandals and religious controversy . 
