Macrinus belonged to the conspirers against Caracalla, and was quickly accepted as emperor in 217. He made a compromise with the Armenians, by accepting Tiridates II, son of Khosrov, as king of Armenia. The Parthians had conquered most of Roman Mesopotamia in the meanwhile. Macrinus was defeated by the Parthians near Nisibis in 217, and made peace with king Artabanus IV on unfavourible terms. The Romans were very displeased that Macrinus lost from a weaker enemy. A conspiracy in 218, by the Severan family quickly made an end to his reign and life.