The Tetrarchy was the system instituted by Roman emperor Diocletian in 293 AD to govern the ancient Roman Empire by dividing it between two emperors, the augusti, and their junior colleagues and designated successors, the caesares.

Diocletian also restructured the Roman government by establishing the Tetrarchy, a system of rule in which four men shared rule over the massive Roman Empire. The empire was effectively divided in two, with an Augustus and a subordinate Caesar in each half.