Marcus Opellius Macrinus was born c.165 AD in Mauretania-Caesarea to parents in the Roman equestrian class. His education allowed him to eventually join the senatorial class. He was a respected lawyer and enjoyed becoming an important bureaucrat under Septimius Severus. Under Caracalla, he was appointed prefect of the Praetorian Guard.
Caracalla clearly trusted Macrinus to a great extent, but began to make changes when it was rumored a prophesy told that Macrinus would depose the emperor and take the position for himself. Caracalla reassigned some of the staff of Macrinus, but must not have been aware of the full prophecy, since Macrinus still held his position.
In 217, Caracalla, Macrinus and the Praetorian Guard were in the eastern provinces, preparing to campaign against the Parthians. In April, possibly on the 8th, Caracalla, his personal bodyguard and Macrinus, went to a temple of Luna near the site of the Battle of Carrhae. On the way, Caracalla was murdered and his body returned from the temple, along with a dead guard who Macrinus claimed killed the emperor.
By April 11, Macrinus proclaimed himself emperor and elevated his son, Diadumenian as caesar. Macrinus added Severus to his name and added Antoninus to his son’s to give the air of legitimacy to his claim to the throne and the stability of the Antonine period to his son. The Senate confirmed him as emperor, making him the first equestrian rank born to ever accomplish the task.
Caracalla’s mother, Julia Domna, still lived and although initially was left in peace, Macrinus ordered her to leave Antioch when she began conspiring with the military. She disobeyed and instead starved herself to death.
Macrinus looked to avoid military conflicts when possible, instead reconciling with some of the enemies engaged under the previous Severans. He returned Dacian hostages taken by Caracalla. He also granted the Armenian throne to Tiridates and released the new king’s father, whom Caracalla had imprisoned. He couldn’t avoid hostilities with the Parthians and engaged them near Nisibis. The conflict was a draw and Rome was forced to pay a crippling 200 million sesterces to Artabanus IV for peace.
The purity of the silver denarius under Macrinus was restored to 58% from 51.5% and the weight was increased from 1.66g to 1.82g. This helped to restore some financial stability in the coinage.
Although Macrinus enjoyed some initial popularity during his reign, seeing monuments like the Capitoline Temple in Volubilis built, it didn’t last long. He didn’t visit Rome after being elevated to emperor and storms caused widespread damage in the city that the prefect was unable to restore to the satisfaction of the populace. Macrinus also was losing the military, since he cut back on the privileges they enjoyed under Caracalla. He also installed a pay scale where new recruits were paid less than veterans.
Some of the other Severan women banded together to plot against Macrinus. Julia Maesa (Caracalla’s aunt) and her daughters, Julia Soaemias and Julia Mamaea used their influence over the cult of the sun-god El-Gabal to proclaim the son of Soaemias, Elagabalus, as the illegitimate son of Caracalla and therefore the rightful heir of the throne. On May 18, Elagabalus was proclaimed emperor in the camp of Legio III Gallica stationed at Raphana. They marched on Macrinus at Antioch on June 8, 218 AD, and soundly defeated him. Macrinus abandoned his forces and fled, but was later caught and executed in Cappadocia. Diadumenian was sent to the court of the Parthians for safety, but was caught at Zeugma and also executed.