What governing system did Diocletian establish in the Roman Empire in 293 CE?

Diocletian established the Tetrarchy in the Roman Empire in 293 CE.

The name Tetrarchy means “rule by four.” Diocletian created a system with two senior emperors, called Augusti, and two junior emperors, called Caesares. Each ruler governed a portion of the empire while presenting the arrangement as a coordinated imperial college.

The system responded to the empire’s enormous size and repeated military crises during the third century. Multiple emperors could command armies near threatened frontiers, while planned succession was intended to reduce civil wars.

The Tetrarchy did not remain stable. Diocletian abdicated in 305 CE, but rival claims soon produced new conflicts. Constantine the Great eventually defeated his competitors and became sole ruler. Even after the Tetrarchy collapsed, Diocletian’s division of imperial administration influenced the later separation between eastern and western Roman governments.