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The Tetrarchs, a porphyry sculpture sacked from a Byzantine palace in 1204, Treasury of St. Marks,
The Tetrarchs, a porphyry sculpture sacked from a Byzantine palace in 1204, Treasury of St. Marks, Venice

Tetrarchy (Greek: "leadership of four people"; cognate with the Latin Quadrumvirate, "government by four men"). While the term can be applied to any system of government were power is divided between four individuals, 'The Tetrarchy' most commonly applies to the system of Roman government insituted by the emperor Diocletian in 293 and lasted until c.313. The establishment of the Tetrarchy usually marks the resolution of the Crisis of the Third Century.


Creation of the Tetrarchy

The first phase (sometimes referred to as the Dyarchy, 'the 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 Caesares (one responsible to each Augustus) - Galerius and Constantius Chlorus. The two Caesares were intended as the future successors to the two Augusti. The first Tetrarchy was therefore created.

Tetrarchic regions and capitals

Missing image
Map of the Roman empire c.350, showing the praetorian prefectures of Gaul, Italy, Illyricum and Oriens, roughly analagous to the four Tetrarchs' zones of influence

The four Tetrarchs based themselves not at Rome but in other cities closer to the frontiers, mainly intended as headquarters for the defence of the empire against bordering rivals (notably Sassanian Persia) and barbarians (mainly Germanic and Berber tribes). These centres are known as the 'Tetrarchic capitals'. Although Rome ceased to be an operational capital, it continued to be nominal capital of the entire empire, not reduced to a province but controlled under the Prefect of the City (praefectus urbis).

The four Tetrarchic capitals were:

  • Nicomedia in northwestern Asia Minor (modern Izmit in Turkey), a base for defence against invasion from the Balkans and the Sassanids. Nicomedia was the capital of Diocletian.
  • Sirmium in the Slavonia region of modern Croatia, and near Belgrade, on the Danube border. Sirmium was the capital of Galerius.
  • Mediolanum (modern Milan, near the Alps). Mediolanum was the capital of Maximian.
  • Augusta Treverorum (modern Trier, in Germany, near the Rhine). Augusta Treverorum was the capital of Constantius Chlorus.

Aquileia, a port on the Adriatic coast, and Eburacum (modern York, in northern England near the Celtic tribes of modern Scotland and Ireland), were also significant centres for Maximian and Constantius respectively.

In terms of regional jurisdiction there was no precise division between the four Tetrarchs, and this period did not see the Roman state actually split up into four distinct mini-empires. Each emperor had certain zones of influence within the Roman Empire, but no more. In the West, the Augustus Maximian controlled the provinces west of the Adriatic Sea and the Syrtis, and within that region his Caesar, Constantius, controlled Gaul and Britain. In the East, the arrangements between the Augustus Diocletian and his Caesar , Galerius, were much more flexible. However, it appears that some contemporary and later writers, such as the Christian author Lactantius, and Sextus Aurelius Victor (who wrote about fifty years later and from uncertain sources), misunderstood the Tetrarchic system in this respect, believing it to have involved a stricter division of territories between the four emperors.

Public image

Although power was shared in the Tetrarchic system, the public image of the four emperors in the imperial college was carefully manipulated to give the appearance of a united empire (patrimonium indivisum). This was especially important after the civil war of the third century.

The Tetrarchs appeared identical in all official portraits. Coinage dating from the Tetrarchic period depicts every emperor with identical features - only the inscriptions on the coins indicate which one of the four emperors is being shown. The porphyry sculpture (pictured above), now embedded in the wall of St. Mark's Basilica in Venice, shows the Tetrarchs again with identical features and wearing the same military costume.


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. While Aurelian and Probus were prepared to accompany their armies thousands of miles between war regions, this was not an ideal solution. 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). All members of the imperial college, on the other hand, were of essentially equal rank, despite two being senior emperors and two being junior; their functions and authorities were also equal.

Under the Tetrarchy a number of important military victories were secured. Both the Dyarchic and the Tetrarchic system therefore allowed an emperor to personally direct and remain in control of campaigns simultaneously on more than just one front. Thus in 296 Galerius crushed the Persians in battle and Constantius defeated the British usurper Allectus.

Fall of the Tetrarchy

Missing image
The Battle of the Milvian Bridge, depicted in a fresco by Raphael

Confusion and collapse

In 305 both Diocletian and Maximian abdicated. The Caesares, Galerius and Constantius Chlorus, were both raised to the rank of Augustus, and two new Caesares were appointed: Maximinus (Caesar to Galerius) and Flavius Valerius Severus (Caesar to Constantius). These four formed the second Tetrarchy. However, the system broke down very quickly thereafter. When Constantius died in 306, Galerius promoted Severus to Augustus while Constantine I was proclaimed Augustus to succeed his father Constantius, by his father's troops. At the same time, Maxentius, the son of Maximian, resented having been left out of the new arrangments, defeated Severus before forcing him to abdicate and then arranging his murder in 307. Maxentius and Maximian then declared themselves both Augusti. By 308 there were therefore no less than four claimants to the rank of Augustus (Galerius, Constantine, Maximian and Maxentius), and one to that of Caesar (Maximinus).

In 308 Galerius, together with the retired emperor Diocletian and the supposedly-retired Maximian, called an imperial 'conference' at Carnutum on the River Danube. At Carnutum it was agreed that Licinius would become Augustus in the West with Constantine as his Caesar. In the East, Galerius remained Augustus and Maximinus remained his Caesar. Maximian was to retire, and Maxentius was declared a usurper. This agreement proved disastrous. Maxentius had become de facto ruler of Italy and Africa by 308 anyway, even if he was deprived of imperial rank. Neither Constantine or Maximinus - who had both been Caesares since 305 - were prepared to tolerate the promotion of the Augustus Licinius as their superior.

After an abortive attempt to placate both Constantine and Maximinus with the meaningless title filius Augusti (son of the Augustus), they both had to be recognised as Augusti in 309. However, four full Augusti all at odds with each other did not bode well for the Tetrarchic system.

End of the Tetrarchy

Between 309 and 312 most of the claimants to the imperial office died or were killed in various internecine wars. Constantine arranged Maximian's death by strangulation in 310. Galerius died naturally in 311. Maxentius was defeated by Constantine at the Battle of the Milvian Bridge in 312 and subsequently killed. Maximinus committed suicide at Tarsus in 313 after being defeated in battle by Licinius.

By 313, therefore, there were only two remaining emperors: Constantine in the West and Licinius in the East. The Tetrarchic system was at an end, although it took until 324 for Constantine to finally defeat Licinius, reunite the two halves of the Roman empire and declare himself sole Augustus.


Although the Tetrarchic system only lasted until c. 313, many aspects survived. the four-fold regional division of the empire continued in the form of praetorian prefectures, each of which was overseen by a praetorian prefect and subdivided into administrative dioceses. The notion of consortium imperii, the sharing of imperial power, was to reappear repeatedly. The idea of the two halves, the East and the West, re-emerged and eventually resulted in the division into two separate Roman empires.

Other Tetrarchies

  • Tetrarchies in the ancient world existed in both Thessaly and Galatia.
  • The unstable constellation of Jewish principalities in Roman Palestine : for instance, the kingdom of Galilee under Herod Antipas was a tetrarchy.

See also

Template:Epochs of Roman Emperors


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