Diocletian's Tetrarchy Reform

Timeline

1. 284–286Nicomedia · BithyniaAfter acceding in 284, Diocletian appointed Maximian as co-ruler, initially forming an east-west division of rule and laying the institutional groundwork for the later Tetrarchy.
2. 293Rome · LazioDiocletian appointed Galerius and Constantius Chlorus as Caesars, forming a four-ruler structure of two Augusti and two Caesars that clarified imperial succession and the division of frontier defense duties.
3. 293–305Throughout the Roman Empire · Roman EmpireUnder the Tetrarchy framework, imperial provinces were redivided into nearly twenty administrative regions, civil and military authority were separated, frontier legions were redeployed, and currency and tax reforms were introduced to stabilize imperial finances.