Diarchy (from Greek δι-, di-, "double", and -αρχία, -arkhía, "ruled"), duarchy, or duumvirate (from Latin duumvirātus, "the office of the two men") is a form of government characterized by corule, with two people ruling a polity together either lawfully or de facto, by collusion and force. The leaders of such a system are usually known as corulers.