Constitution of the late Roman Empire

The constitution of the late Roman Empire was an unwritten set of guidelines and principles passed down, mainly through precedent, which defined the manner in which the late Roman Empire was governed. As a matter of historical convention, the late Roman Empire emerged from the Roman Principate (the early Roman Empire), with the accession of Diocletian in AD 284, his reign marking the beginning of the Tetrarchy.

Source: Wikipedia — Constitution of the late Roman Empire (CC BY-SA 4.0)