Roman Emperor (Dominate) - Tetrarchy

Tetrarchy

The Tetrarchy was a system established by Diocletian to facilitate effective government of the Empire.

After acceding to power in 284, Diocletian decide to share the load of government with his friend Maximian, whom he appointed co-regent in 286. Maximian was to use the title Caesar, while Diocletian alone was Augusti. Diocletian focused on the eastern parts of the Empire while Maximian focused on the west.

In 293, this system was further developed into the Tetrarchy: Maximian was elevated to the rank of Augustus and both Augusti appointed junior sub-emperors with the title Caesar.

There were two senior emperors (titled Augusti), one for the West and one for the East, and two junior sub-emperors (titled Caesares), one for each senior emperor. When the Augusti left office for whatever reason, the Caesares would become Augusti and appoint their own Caesares; the retired Augusti took the title senior augustus and were styled Patres Imperatorum et Caesarum ("Fathers of the Imperators and of the Caesars").