Roman Tetrarchy
For a period, the empire was ruled as a tetrarchy.
Contents
History
As part of Diocletian's reforms, he divided the imperial government. Direct governance was geographically divided between east and west, each having an independent emperor (augustus). Each also had an heir apparent and 'junior emperor' (caesar).
This administrative division of the empire into quarters was overseen by the praetorian prefects.
The orderly succession of the tetrarchy lasted until Constantine usurped the western imperial title. Claims to the succession of the tetrarchy continued until 324.