The Roman Tetrarchies

by Jim Phelps

The Roman Tetrarchies

Western Rulers Year
Eastern Rulers

285Diocletian seizes the empire from Carinus, the last of the family of Carus.
286(April 1) Diocletian names his friend Maximianus as co-emperor. Diocletian takes charge of the east from Nicomedia and wages war against the Sasanian Persians. Maximianus fights against tribes in Gaul.
Facing a large problem of pirates along the northwestern coast of France, Maximianus appoints one of his generals, Carausius, to command a fleet to clear the seas.
287Carausius soon realizes that it is more profitable to wait until after the pirates had plundered and area before attacking them, and eventually turns to actual piracy himself. He then defeats loyalist forces in in the province of Britain and establishes himself as ruler there, along with a small part of Gaul.
293Realizing the empire is too large and beset by too many foes to be managed by two rulers, Diocletian reforms the rulers into a tetrarchy. Though Diocletian is still the senior ruler, he and Maximianus each appoint their praetorian prefects as caesars under them, each with several provinces to administer and defend. Diocletian continues to rule from Nicomedia with Galerius governing from Thessalonika. Maximianus rules the west from Mediolanum with Constantius I Chlorus governing from Treveri.
293Constantius is given the task to defeat Carausius. He regains control over the rebel Gallic province. Carausius is murdered by his chief minister Allectus, who then declares himself emperor.
Diocletian reforms the coinage. At the beginning of his reign he was issuing the standard "Aurelianus", or antoninianus under the reformed standard of Aurelian. Under the reforms the base metal coinage is replaced with a follis with a very generic "blocky"/militaristic head. Accompanying this is a smaller coin with a radiate bust called a "post-reform radiate". These are easily distinguishable from the aurelianus by the loss of the "XXI" or "KA" in the exergue.
296Constantius I invades and recovers Britain, defeating and killing Allectus.
305(May 1) After 20 years of successful rule, the senior emperors jointly abdicate and retire, allowing Constantius and Galerius to elevate in rank to Augusti. They in turn appoint two new Caesars - Severus II in the west under Constantius, and Maximinus in the east under Galerius. Though Severus was an able military man, Maximinus was an inexperienced young relative of Galerius most likely intended to be simply a puppet. It soon becomes obvious that the tetrarchy system only worked under a strong senior leader - since Diocletian is no longer keeping a stern rule, the emperors begin squabbling.
306(Summer) Constantius Chlorus dies at York, while campaigning in Britain against the Picts. His soldiers declare his son, Constantine I as the new augustus. Though this had been the typical method during the 3rd century, it is against the principals of the tetrarchy as Severus II should have then been elevated. In order to avoid civil wars of succession, Galerius compromises and allows Constantine to be Caesar of the west, while Severus II is elevated to the western Augustus.
In an effort to raise funds, Galerius increases the tax rate and also removes the traditional tax exemptions for Roman citizens. In response the people of Rome raise Maxentius, the son of the former emperor Maximianus, as their augustus. He initially tries to negotiate a peaceful settlement, but soon accepts the revolt and also calls his father out of retirement to join his as co-Augustus. Galerius orders the "official" western Augustus, Severus II, to put down the revolt.

307(Summer) Severus II fails to put down the revolt in Rome and flees to Ravenna, where he is captured and executed. Maxentius and Maximianus increase their holdings to include all of Italy, as well as Spain and North Africa. Maximianus goes to the court of Constantine I at Treveri and convinces him to join the revolt against the eastern rulers. Constantine accepts, and also assumes the rank of Augustus. To cement this alliance Constantine is married to Fausta, the daughter of Maximianus. Maxentius and Maximianus soon begin quarreling, and Maximianus leaves his son to join the court of Constantine.
308Galerius calls the Conference of Caruntum, which is chaired by the founder of the tetrarchy system, Diocletian. Maximianus is forced to abdicate again, and Licinius (a friend of Galerius) is appointed Augustus of the west. Constantine is returned to the lower rank of Caesar, and Maxentius is declared a public enemy (yet he still manages to keep control over his holdings). Both Constantine and Maximinus II were unhappy with the results of this negotiation since Licinius (who had never been a Caesar) was promoted over them, and in response Galerius eventually creates a meaningless title of "Filius Augustorum" for them. By 310 both are made Augusti again.

310(Spring) Once again Maximianus stages a revolt against his son-in-law Constantine and declares himself emperor from Massilia. Constantine quickly captures and executes him.
311Galerius dies and Maximinus moves up in rank to senior western emperor, correspondingly moving his court to Nicomedia. Licinius leaves the west and begins rule from Thessalonika, yet retains the title of Augustus. This leaves Constantine as the sole "official" ruler of the west, though the rebel Maxentius still holds much territory.
312The outlawed Maxentius moves against a new rebel in his holdings, Domitius Alexander in Carthage. Upon returning to Rome he finds the forces of Constantine invading from the north. He is defeated and killed at the battle of Milvian Bridge (28 October) leaving Constantine as the sole ruler in the west.
313Constantine and Licinius meet and form an alliance to rule together. Maximinus leads an army against Licinius in Macedonia and Thrace but is defeated on April 30. He dies a short time later.
316Constantine rules in the west and Licinius in the east, but Constantine invades Licinus' territory. Licinius names Valens as his co-ruler. They come to a truce soon, and Valens is put to death.
317Three new Caesars were elevated from their families of the Augusti - Crispus and Constantine II in the west, and Licinius II in the east.
324Constantine invades again, and Licinius is defeated first at the battle of Hadrianopolis in July. Licinius names Martinian as co-ruler, but is defeated again, and for the last time, in September at the battle of Chrysopolis. in a series of battles Constantine emerges victorious, and eventually both Licinius and Martinian abdicate, though they are executed a year later.