The term Tetrarchy (Greek: "leadership of four [people]") describes any system of government where power is divided among four individuals, but usually refers to the tetrarchy instituted by Roman Emperor Diocletian in 293, marking the end of the Crisis of the Third Century and the recovery of the Roman Empire. This Tetrarchy lasted until c.313, when internecine conflict eliminated most of the claimants to power, leaving Constantine in the West and Licinius in the East.

Creation

The first phase, sometimes referred to as the Diarchy ('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 Caesars (one responsible to each Augustus) - Galerius and Constantius Chlorus.

In 305, the senior emperors jointly abdicated and retired, allowing Constantius and Galerius to be elevated in rank to Augusti. They in turn appointed two new Caesars - Severus II in the west under Constantius, and Maximinus in the east under Galerius. The second Tetrarchy was therefore created.

It is interesting to note that these men were from the Roman provice of Illyria, several in the city of Sirmium, which would become one of the four capitals under this system. From the time of Domitian (81–96), when over half the Roman army was deployed in the Danubian regions, the Illyrian provinces had been the most important recruiting ground of the auxilia and later the legions. In the 3rd century, Romanised Illyrians came to dominate the army's senior officer echelons. Ultimately, the Illyrian officer class seized control of the state itself. In 268, the emperor Gallienus who ruled the Roman Empire as co-emperor with his father Valerian from 253 to 260, and then around 268 was overthrown by a coup d'état organized by a clique of Illyrian senior officers, including his successors Claudius II Gothicus and Aurelian. These men and their successors Probus, Roman Emperor (276–8), was a native of Sirmium in Pannonia, and Diocletian was Roman Emperor (284–305) and his colleagues in what became to be know as the Tetrarchy.

Flavius Valerius Constantius was an emperor of the Western Roman Empire was a Caesar (deputy emperor) in Diocletian's Tetrarchy. His son, Constantine, is best remembered in modern times for the Edict of Milan in 313, which freed Christianity from official Roman persecution. Constantine's sons ruled after his death in 337 until the death of Julian. After that the empire was ruled by the sons and grandson of another Illyrian senior officer, who was born under Diocletian.

Regions and capitals

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 an endless procession from the eastern steppe; many nomadic or elsewhere chased tribes) at the Rhine and Danube. These centres are known as the 'Tetrarchic capitals'. Although Rome ceased to be an operational capital, the 'Eternal City' continued to be nominal capital of the entire empire, not reduced to the status of a province but under its own, unique Prefect of the City (praefectus urbis, later copied in Constantinople).

The four Tetrarchic capitals were:

• Nicomedia in northwestern Asia Minor (modern Izmit in Turkey), a base for defence against invasion from the Balkans and Persia's Sassanids, not Constantinople (given that name at its later refounding), was the capital of Diocletian, the eastern (and most senior) Augustus; in the final reorganisation by Constantine the Great, in 318, the equivalent of his domain, facing the most redoubtable foreign enemy, Sassanid Persia, became the pretorian prefecture Oriens 'the East', the core of later Byzantium.

• Sirmium (modern Sremska Mitrovica) in the Vojvodina region of modern Serbia, and near Belgrade, on the Danube border) was the capital of Galerius, the eastern Caesar; this was to become the Balkans-Danube- prefecture Illyricum.

• Mediolanum (modern Milan, near the Alps), not Rome, was the capital of Maximian, the western Augustus; his domain became "Italia et Africa", with only a short exterior border.

• Augusta Treverorum (modern Trier, in Germany) was the capital of Constantius Chlorus, the western Caesar, near the strategic Rhine border, it had been the capital of Gallic emperor Tetricus I; this quarter became the prefecture Galliae.

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 sub-empires. Each emperor had his zone of influence within the Roman Empire, but little more, mainly high command in a 'war theatre', himself often in the field, while delegating most of the administration to the hierarchic bureaucracy headed by each Tetrarch's Pretorian Prefect, each supervising several Vicarii, the governors-general in charge of another, lasting new administrative level, the civil diocese, of which there were originally twelve, later several were split.For a listing of the provinces, now known as eparchy, within each quarter (known as a pretorian prefecture), see Roman province.

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 managed 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 Portrait of Four Tetrarchs porphyry sculpture (pictured at right), now standing at the south-west corner of St. Mark's Basilica in Venice, shows the Tetrarchs again with identical features and wearing the same military costume.

Military successes

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 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. After suffering a defeat by the Persians in 296, Galerius crushed Narseh in 298 - reversing a series of Roman defeats throughout the century - capturing members of the imperial household, a substantial amount of booty and gaining a highly favourable peace treaty, which secured peace between the two powers for a generation. Similarly, Constantius defeated the British usurper Allectus, Maximian pacified the Gauls and Diocletian crushed the revolt of Domitianus in Egypt.

Demise

When in 305 the 20-years reign term of Diocletian and Maximian ended, both abdicated. Their 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 the Great 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 arrangements, defeated Severus before forcing him to abdicate and then arranging his murder in 307. Maxentius and Maximian both then declared themselves Augusti. By 308 there were therefore no fewer than four claimants to the rank of Augustus (Galerius, Constantine, Maximian and Maxentius), and only 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 Carnuntum on the River Danube, which 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 an usurper. This agreement proved disastrous: by 308 Maxentius had become de facto ruler of Italy and Africa anyway, even if he was deprived of imperial rank; neither Constantine nor 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', which could have been an alternative title for Caesar, as either implied the right to succeed), 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.

Between 309 and 313 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 remained only two 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.

Timeline

285 - 293

;Augusti

:Oriens Diocletian (285 - 293)

:Occidens Maximian (285 - 293)

293 - 305

;Augusti

:Oriens Diocletian (285 - 305)

:Italia et Africa Maximian (285 - 305)

;Caesars

:Illyricum Galerius (293 - 305)

:Gallia et Hispaniae Constantius Chlorus (293 - 305)

;Augustus

:Britania Carausius (286 - 293)

:Allectus (293 -296)

;Usurpers

:Amandus et Aelianus - leaders of the Bagaudae in Gaule (285-286)

:Sabinus Iulianus - Africa Zeugitana (circa 285-293)

:Domitius Domitianus - Aegyptus (296 - 297)

:Aurelius Achilleus - Aegyptus (297 - 298)

:Eugenius - Syria Coele (303/304)

305 - 306

;Augusti

:Illyricum Galerius (305 - 306)

:Gallia, Hispaniae et Britannia Constantius Chlorus (305 - 306)

;Caesars

:Oriens Maximinus Daia (305 - 306)

:Italia et Africa Severus (305 - 306)

306 - 307

;Augusti

:Illyricum Galerius (306 - 307)

:Italia et Africa Severus (306 - 307)

;Caesars

:Oriens Maximinus Daia (306 - 307)

:Gallia, Hispaniae et Britannia Constantine I (306 - 307)

;Caesars

:Roma Maxentius (307)

307 - 313

;Augusti

:Illyricum Galerius (307 - 311)

:Gallia, Hispaniae et Britannia Constantine I (307 - …)

:Trhacia et Pontus to Taurus Licinius (308 - …)

:Italia Maxentius (307 - 312)

:Oriens from Taurus to Aegyptus Maximinus Daia (310 - 313)

:Italia Maximian (307 -310)

;Caesars

:Oriens from Taurus to Aegyptus Maximinus Daia (307 - 310)

;Usurpers

:Domitius Alexander - Africa (308 - 311) Constantine's Allied

313 - 324

;Augusti

:Oriens Licinius (313 - 324)

:Occidens Constantine I (313 - 324)

:Oriens Sextus Martinianus (324)

;Caesars

:Italia Bassianus (313 -314)

:Illyricum Valerius Valens (314 - 316)

:Oriens Licinius the Younger (317 - 324)

:Occidens Crispus (317 -326)

324

;Augustus

:Constantine I

Legacy

Although the Tetrarchic system as such only lasted until c. 313, many aspects survived. The fourfold 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, and often reappeared in the title of the military supra-provincial command assigned to a magister militum.

The pre-existing notion of consortium imperii, the sharing of imperial power, and/or the notion that an associate to the throne was the designated successor (possibly conflicting with the notion of hereditary claim by birth or adoption), was to reappear repeatedly.

The idea of the two halves, the East and the West, re-emerged and eventually resulted in the permanent de facto division into two separate Roman empires after the death of Theodosius I (though it is important to remember that the Empire was never formally divided, Emperors of East and West legally ruling as one imperial college till the fall of Rome's western empire left Byzantium, the 'second Rome', sole direct heir).

Other examples

• Tetrarchies in the ancient world existed in both Thessaly (in northern Greece) and Galatia (in central Asia Minor; including Lycaonia).
• The constellation of Jewish principalities in Roman Palestine: for instance, Herod Antipas ruled Galilee and Perea as a tetrarch (so styled in the gospel of Matthew, but rendered as king in the Gospel of Mark).

See also

• Notitia dignitatum, a later document from the imperial chancery

References

External links

• A detailed chronology of the tetrarchy from Diocletian to Constantine
• A chart showing the tetrarchy from Diocletian to Constantine