Editing Tetrarchy (section)

==Creation<!--Linked from 'Byzantine Empire'-->==
The first phase, sometimes referred to as the [[diarchy]] ("rule of two"), involved the designation of the general [[Maximian]] as co-emperor—firstly as ''[[Caesar (title)|caesar]]'' (heir apparent) in 285, followed by his promotion to ''augustus'' in 286. [[Diocletian]] took care of matters in the eastern regions of the empire while Maximian similarly took charge of the western regions. In 293, Diocletian thought that more focus was needed on both civic and military problems, so with Maximian's consent, he expanded the imperial college by appointing two ''caesares'' (one responsible to each ''augustus'')—[[Galerius]] and [[Constantius I]].<ref>The chronology has been thoroughly established by Kolb, ''Diocletian'', and Kuhoff, ''Diokletian''.</ref>

In 305, the senior emperors jointly abdicated and retired, allowing Constantius and Galerius to be elevated in rank to ''augustus''. They in turn appointed two new ''caesares''—[[Flavius Valerius Severus|Severus II]] in the west under Constantius, and [[Maximinus II|Maximinus]] in the east under Galerius—thereby creating the second Tetrarchy.