One of the greatest problems facing emperors in the Third Century Crisis was that they were only ever able to personally command troops on one front at any one time. Furthermore, it was risky for an emperor to delegate power in his absence to a subordinate general, who might win a victory and then be proclaimed as a rival emperor himself by his troops (which often happened). The Roman Emperor Diocletianus created a new state organization, dividing the empire in four portions, each ruled by a member of the imperial college. These leaders were of essentially equal rank, despite two being senior emperors and two being junior; their functions and authorities were also equal. The system was called "Tetrarchy"

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 (junior emperor) 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, feeling more focus was needed on both civic and military problems, Diocletian, with Maximian's consent, expanded the imperial college by appointing two Caesars (one responsible to each Augustus) — Galerius and Constantius Chlorus.

Under the Tetrarchy a number of important military victories were secured. Both the Dyarchic and the Tetrarchic system ensured that an emperor was nearby to every crisis area to personally direct and remain in control of campaigns simultaneously on more than just one front. Decisive victories were scored against the most dangerous enemies of the Empire: Persians, Goths, Sarmatians and Alamanni, securing the frontiers and strenghtening the Empire.