Diocletian ended Rome's period of political instability known as the Crisis of the Third Century. After consolidating power, he moved to create a political settlement guaranteeing future stability for the empire. Constant civil wars and barbarian incursions flummoxed emperors, strained resources, and led to several succession crises. As a result, Diocletian hoped to establish four administrative centers designed to run and protect the empire. In the end, Diocletian established a tetrarchy of four emperors to administer the empire, ensure smooth succession, and protect the borders.
The third century witnessed the Roman Empire's collapse. Barbarians swarmed over the border, as many as 80 men claimed the imperial throne in a 50 year period, and the military struggled to meet foreign and domestic threats. Diocletian built on his predecessors efforts to bring stability and finally succeeded. However, the emperor worried about the future. He decided to create a lasting political settlement designed to reinforce the empire against itself and its enemies.
Diocletian elevated Maximian to co-emperor. This in itself was not unusual. Marcus Aurelius and several other emperors had served with others while holding most of the power. This arrangement allowed for an easy succession in the event of the death of the senior emperor. In 286, Maximian received another promotion. Diocletian served as the senior partner while Maximian held the title "Augustus." Augustus Maximian handled duties in the west while Diocletian headed east to deal with the Sarmatians and other tribes.
In 293, Diocletian decided to split the dual emperorship into four. Galerius and Constantius Chlorus were promoted to junior emperors, or "Caesar." As a result, Rome now had two senior emperors and two junior emperors administering the empire. Each emperor controlled about a quarter of the empire. Gaul and Britain, Italy and the west, the Balkans, and Egypt and the east each represented an imperial zone.
Each emperor ruled from his own capitol. This allowed the tetrarchy to govern with little interference from the Roman Senate. This arrangement helped centralize authority within the emperor and further watered down republican traditions. On the other hand, emperors could react quicker to events, receive information faster, and more effectively govern. More practically, the four power solution allowed an emperor to mobilize his military and march on a threat faster than under the old system.
The tetrarchy did not survive Diocletian's retirement. In 305, the two senior emperors abdicated and retired. The two junior emperors automatically elevated to Augustus and two new Caesars selected. Diocletian designed the system to help with succession upon the death or retirement of an emperor. However, the system began to falter in 306. Constantius died in 306 and his troops proclaimed his son, Constantine, Augustus. Meanwhile, the system promoted Severus to the same position. However, Maximian's son, Maxentius, murdered Severus. By 313, the Tetrarchy ceased to exist when Licinius and Constantine split the empire in two. In 324, Constantine eliminated his rival returning the empire to rule by a single emperor.
Diocletian hoped to improve imperial governance, military readiness, and succession. As a result, he created the tetrarchy to ease imperial burdens. He established four emperors in four capitals in order to increase military response time, nip potential rebellions early, and react to political events quickly. When one emperor died or retired, another could move in to take his place without civil war. However, the system collapsed without his force of personality. Diocletian retired in 305 and the tetrarchy died in 313.