Emperor of Rome from 217 A.D. to 218 A.D. Marcus Opellius Macrinus was a most notable emperor not for the fact that during his short 14 month reign he never set foot in Rome (he was off fighting in the East), but for the fact that he was the first emperor who was neither a senator, nor of senatorial blood when he became emperor. He succeeded Caracalla, the stupendously useless son of Septimus Severus. Macrinus was never able to shake rumors that he had ordered Caracalla's murder, which was not surprising, since he had ordered Caracalla's murder.

Born in Caesarea around 165, the well-educated Macrinus worked his way up as a bureaucrat during Severus' reign, and was appointed prefect of the Praetorian Guard along with a soldier by the name of Adventus by Caracalla after his father's death. While the two were off fighting in the East, rumors began that Macrinus was jockeying for the position of Emperor. An oracle corroborated the rumors for Caracalla, who immediately began reassigning members of Macrinus' staff. Macrinus, who was not planning to kill Caracalla, began planning to kill Caracalla because he believed (rightly) that his life was probably in danger, and that he could exert his influence in Rome from the Eastern campaigns. Caracalla went to a temple in Carrhe with a hand-picked group of bodyguards, and came out dead along with one of the bodyguards, who was blamed for the murder. Few people believed the story.

Macrinus was proclaimed Emperor by the troops on April 11, 217, sent Adventus to Rome as urban prefect, and named his son Diadumenian his heir soon afterwards. He then got his ass handed to him by the Parthians at Nisbis, which hurt the morale of his troops, and lost much popularity by not returning to Rome, which experienced fire and flood after a storm in August. Adventus, who had been incompetent, was replaced. Between grumbling troops and dissatisfied citizenry, Elagabalus, the 14 year old grandson of one of Caracalla's aunts, successfully lead a revolt against Macrinus that began May 15, 218 and ended on June 8, with Macrinus' forces defeated at Antioch. Macrinus and Diadumenian (who had been promoted to co-Emperor by Macrinus when the revolt began) were both executed.