Tetrarchy (Greek: "leadership of four [people] ") can be applied to any system of government where power is divided between four individuals. The term is usually used to refer to the tetrarchy instituted by Roman 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 and the recovery of the Roman Empire.

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 "Caesars" (one responsible to each "Augustus") - Galerius and Constantius Chlorus.

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 first Tetrarchy was therefore created.

Tetrarchic 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 Eternal 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 excentric capital of Constantius Chlorus, the western "Caesar", near the strategic Rhine border, hence it had before 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.


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.

Fall of the Tetrarchy

Confusion and collapse

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 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 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.

End of the Tetrarchy

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.


285 - 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 "Domitius Domitianus" - "Aegyptus" "(297)" "Aurelius Achilleus" - "Aegyptus" "(297 - 298)"

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" Licinius (308 - ...) || "Italia" Maxentius (307 - 312)

"Oriens from Taurus" Maximinus Daia (310 - 313) || "Italia" Maximian (307 -310)
* Caesars "Oriens from Taurus" 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 "Illyricum" Valens (314 - 316) || "Italia" Bassianus (313 -316)

"Oriens" Licinius the Younger (317 - 324) || "Occidens" Crispus (317 -326)

*Augustus Constantine I


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 — in the theoretical republic still unconstitutionalFact|date=December 2007 — 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).

Lesser Tetrarchies

* 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).
*At a number of modern American universities, tetrarchy is the preferred format for student government, based on the model established at the University of Virginia with the governing body known as HJM.Facts|date=January 2008

ee also

* Augustus (honorific)
* Caesar (title)
* Consortium imperii


*cite book
last = Barnes
first = Timothy D.
title = [http://www.hup.harvard.edu/catalog/BARCON.html Constantine and Eusebius]
publisher = Harvard University Press
date = 1984
pages =
id = ISBN 0-674-16531-4

*cite book
last = Bowman
first = Alan
title = The Cambridge Ancient History Volume 12, The Crisis of Empire, AD 193-337
publisher = Cambridge University Press
date =2005
pages =
url = http://www.cambridge.org/catalogue/catalogue.asp?isbn=0521301998
id = ISBN 0-521-30199-8

*cite book
last = Corcoran
first = Simon
authorlink=Simon Corcoran
title = The Empire of the Tetrarchs, Imperial Pronouncements and Government AD 284-324
publisher = Oxford University Press
date = 2000
pages =440 pages
url =http://www.oup.com/uk/catalogue/?ci=9780198153047
isbn =0-19-815304-X

*cite book
last =Rees
first =Roger
title = [http://www.eup.ed.ac.uk/edition_details.aspx?id=11615 Diocletian and the Tetrarchy]
publisher = [http://www.eup.ed.ac.uk Edinburgh University Press]
date =2004
pages =
isbn =0-7486-1661-6

External links

* [http://www.fourthcentury.com/index.php/evolution-tetrarchy A detailed chronology of the tetrarchy from Diocletian to Constantine]
* [http://www.fourthcentury.com/notwppages/tetrarchy-table.htm A chart showing the tetrarchy from Diocletian to Constantine]


*Notitia dignitatum, a later document from the imperial chancery
*Pauly-Wissowa, Realencyclopädie der Klassischen Altertumswissenschaft

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Look at other dictionaries:

  • Tetrarchy — Tet rarch*y, n.; pl. {Tetrarchies}. [L. tetrarchia, Gr. ?: cf. F. t[ e]trarchie.] (Rom. Antiq.) The district under a Roman tetrarch; the office or jurisdiction of a tetrarch; a tetrarchate. [1913 Webster] …   The Collaborative International Dictionary of English

  • tetrarchy — [te′trär kāt΄, tē′trär kit; te′trär΄kit, tē′truar΄kitte′trär΄kē, tē′trär΄kē] n. pl. tetrarchies 〚L tetrarchia < Gr〛 1. the rule or territory of a tetrarch 2. government by four persons: Also tetrarchate [te′trär kāt΄, tē′trär kit; te′trär΄kit,… …   Universalium

  • tetrarchy — [te′trär kāt΄, tē′trär kit; te′trär΄kit, tē′truar΄kitte′trär΄kē, tē′trär΄kē] n. pl. tetrarchies [L tetrarchia < Gr] 1. the rule or territory of a tetrarch 2. government by four persons: Also tetrarchate [te′trär kāt΄, tē′trär kit; te′trär΄kit …   English World dictionary

  • tetrarchy — I. ˈte.ˌträrkē, ˈtē.ˌ noun ( es) Etymology: Middle English tetrarchie, from Latin tetrarchia, from Greek, from tetrarchēs tetrarch + ia y 1. : the district, office, or jurisdictio …   Useful english dictionary

  • tetrarchy — noun (plural chies) Date: 15th century government by four persons ruling jointly …   New Collegiate Dictionary

  • tetrarchy — noun Historically, an empire that was ruled by four rulers. Syn: quadrumvirate …   Wiktionary

  • Tetrarchy —    The term means the rule of four, referring to the new form of government established by Diocletian (q.v.) in 293. Two augustii, Diocletian in the East and Maximian (q.v.) in the West, ruled each half of the empire. Each augustus (q.v.) had a… …   Historical dictionary of Byzantium

  • tetrarchy — government by four people Forms of Government …   Phrontistery dictionary

  • Tetrarchy (Judea) — The Tetrarchy of Judea was formed following the death of Herod the Great in 4 BC, when his kingdom was divided between his sons as an inheritance. It persisted into the first century, until the kingdom was re united under Herod Agrippa I in… …   Wikipedia

  • Civil Wars of the Tetrarchy (306–324) — The Civil Wars of the Tetrarchy were a series of conflicts between the co emperors of the Roman Empire, starting in 306 AD with the usurpation of Maxentius and the defeat of Severus, and ending with the defeat of Licinius at the hands of… …   Wikipedia

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