Marcus Opelius Macrinus was born in 164 at Caesarea in Mauretania (now Cherchell, Algeria). Although coming from a humble background not dynastically related to the Severan dynasty; he rose through the imperial household until, under Caracalla, he was made prefect of the Praetorian Guard. On account of the cruelty and the treachery of the emperor, Macrinus became involved in a conspiracy to kill him and ordered the Praetorian Guard to do so. On April 8, 217, Caracalla was assassinated travelling to Carrhae. Three days later, Macrinus was declared "augustus".