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Roman imperial dynasties
The Tetrarchy
Diocletian as Augustus 284–286
-with Maximian
as Augustus of the West
-with Galerius and Constantius Chlorus
as Caesares
Maximian as the sole Caesar 285–286
-with Diocletian
as Augustus of the East
-with Galerius and Constantius Chlorus
as Caesares
Galerius and Constantius Chlorus as Caesares 293–305
Galerius and Constantius Chlorus as Augusti of East and West 305–306
-with Severus and Maximinus Daia as Caesares 305–306
Galerius and Severus as Augusti of East and West 306–307
-with Maximinus Daia and Constantine the Great as Caesares 306–307
Galerius and Maxentius as Augusti of East and West 307–308
-with Maximinus Daia and Constantine the Great as Caesares 307–308
Galerius and Licinius as Augusti of East and West 308–311
-with Maximinus Daia and Constantine the Great as Caesares 308–311
Maxentius as usurper in Rome (and Asia Minor 311–312) 308–312
Maximinus Daia and Licinius as Augusti of East and West 311–312
-with Constantine the Great as Caesar (self proclaimed Augustus) 311–312
Licinius and Constantine the Great as Augusti of East and West 312–324
-with Licinius II and Constantine II, Crispus as Caesares 317–324
Preceded by
Crisis of the Third Century
Followed by
Constantinian dynasty

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The term "tetrarchy" (from the Greek τετραρχία "leadership of four [people]")[lower-alpha 1] describes any form of government where power is divided among four individuals, but in modern usage usually refers to the system 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 East and Licinius in the West.


Although the term "tetrarch" was current in antiquity, it was never used of the imperial college under Diocletian. Instead, the term was used to describe independent portions of a kingdom that were ruled under separate leaders. The tetrarchy of Judaea, established after the death of Herod the Great, is the most famous example of the antique tetrarchy. The term was understood in the Latin world as well, where Pliny the Elder glossed it as follows: "each is the equivalent of a kingdom, and also part of one" (regnorum instar singulae et in regna contribuuntur).[1]

As used by the ancients, the term describes not only different governments, but also a different system of government from the Diocletianic arrangements. The Judaean tetrarchy was a set of four independent and distinct states, where each tetrarch ruled a quarter of a kingdom as they saw fit; the Diocletianic tetrarchy was a college led by a single supreme leader. When later authors described the period, this is what they emphasized: Ammianus had Constantius II admonish Julian for disobedience by appealing to the example in submission set by Diocletian's lesser colleagues; Julian himself compared the Diocletianic tetrarchs to a chorus surrounding a leader, speaking in unison under his command. Only Lactantius, a contemporary of Diocletian and a deep ideological opponent of the Diocletianic state, referred to the tetrarchs as a simple multiplicity of rulers.[2]

Much modern scholarship was written without the term. Although Edward Gibbon pioneered the description of the Diocletianic government as a "New Empire", he never used the term "tetrarchy"; neither did Theodor Mommsen. It did not appear in the literature until used in 1887 by schoolmaster Hermann Schiller in a two-volume handbook on the Roman Empire (Geschichte der Römischen Kaiserzeit), to wit: "die diokletianische Tetrarchie". Even so, the term did not catch on in the literature until Otto Seeck used it in 1897.[3]


The first phase, sometimes referred to as the Diarchy ("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.[4]

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 — thereby creating the second Tetrarchy.

Regions and capitals

Map of the Roman Empire under the Tetrarchy, showing the dioceses and 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 an unending sequence of nomadic or displaced tribes from the eastern steppes) at the Rhine and Danube. These centres are known as the Tetrarchic capitals. Although Rome ceased to be an operational capital, Rome continued to be nominal capital of the entire Roman 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 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.
  • Mediolanum (modern Milan, near the Alps) 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 Eboracum (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'. Each Tetrarch was himself often in the field, while delegating most of the administration to the hierarchic bureaucracy headed by his respective Pretorian Prefect, each supervising several Vicarii, the governors-general in charge of another, lasting new administrative level, the civil diocese. For a listing of the provinces, now known as eparchy, within each quarter (known as a praetorian 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

The Tetrarchs, a porphyry sculpture sacked from a Byzantine palace in 1204, now standing at the southwest corner of St Mark's Basilica, Venice

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 3rd 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 Byzantine sculpture Portrait of the Four Tetrarchs (pictured at right) 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 and 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.


Constantine at the battle of the Milvian Bridge, fresco by Raphael, Vatican Rooms.

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When in 305 the 20-year 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, Constantius' son, was proclaimed Augustus by his father's troops. At the same time, Maxentius, the son of Maximian, who also resented being 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. The council 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 even without any imperial rank, and neither Constantine nor Maximinus—who had both been Caesares since 306 and 305 respectively—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", essentially an alternative title for Caesar), 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 civil wars. Constantine forced Maximian's suicide 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.


A chart of the diarchy and tetrarchy from 286 to 305.
A chart of the tetrarchy from 305 to 306, after the retirement of Diocletian and his colleague Maximian, and the accession of Constantius and Galerius.
A chart of the tetrarchy from 306 to 307. After the usurper Maxentius declared himself Caesar, Augustus Severus marched on Rome but was defeated when his troops deferred to Maxentius. Severus was later executed in the same year, 307. Maxentius, and his father and former Augustus, Maximianus (Maximian), declared themselves Augusti later that year.
Maximianus joined the secessionist regime of his son, Maxentius, in Italy. Constantine joined the secessionist alliance by marrying Maximianus' daughter, Fausta, and by supporting Maxentius in Italy. However, Constantine remained neutral with Galerius, but he still took the title of Augustus in the secessionist regime.


Oriens Diocletian (286–293)
Occidens Maximian (286–293)


Oriens Diocletian (286–305)
Italia et Africa Maximian (286–305)
Illyricum Galerius (293–305)
Gallia et Hispaniae Constantius Chlorus (293–305)
Leaders of the Bagaudae in Gaul Amandus and Aelianus (285–286)
Africa Zeugitana Sabinus Iulianus (c. 285–293)
Britania Carausius (286–293)
Britania Allectus (293–296)
Aegyptus Domitius Domitianus (296–297)
Aegyptus Aurelius Achilleus (297–298)
Syria Coele Eugenius (303/304)


Illyricum Galerius (305–306)
Gallia, Hispaniae et Britannia Constantius Chlorus (305–306)
Oriens Maximinus Daia (305–306)
Italia et Africa Flavius Valerius Severus (305–306)


Illyricum Galerius (306–307)
Italia et Africa Flavius Valerius Severus (306–307)
Oriens Maximinus Daia (306–307)
Gallia, Hispaniae et Britannia Constantine I (306–307)
Roma Maxentius (307)


Illyricum Galerius (307–311)
Gallia, Hispaniae et Britannia Constantine I (307–…)
Thracia et Pontus to Taurus Licinius (308–…)
Italia Maxentius (307–312)
Oriens from Taurus to Aegyptus Maximinus Daia (310–313)
Italia Maximian (307–310)
Oriens from Taurus to Aegyptus Maximinus Daia (307–310)
Africa Domitius Alexander (308–311)


Oriens Licinius (313–324)
Occidens Constantine I (313–324)
Oriens Sextus Martinianus (324)
Italia Bassianus (313–314)
Illyricum Valerius Valens (314–316)
Oriens Licinius the Younger (317–324)
Occidens Crispus (317–326)


Constantine I

Other Schematic Summary

1. Tetrarchy till 1. May 305

West ! East
Augusti Maximian Diocletian
Caesares Constantius Chlorus Galerius

2. Tetrarchy till July 306

After the retirement of the two Augusti succeed the both previous Caesares and appoint two new Caesares. Maximinus Daia is the nephew of Galerius Galerius.

West ! East
Augusti Constantius Chlorus Galerius
Caesares Severus Maximinus Daia

3. Tetrarchy till 16. May 307

After the death of Constantius his legions proclamate his son Constantin to be the new Augustus, but Galerius elevates Severus to be the new junior Augustus and compensates Constantin with the grade of Caesar'.

West ! Easten
Augusti Severus Galerius
Caesares Constantin Maximinus Daia

4. Tetrarchy from 18. Novembre 308 to the bgeinning of May 311

After the death of Severus it isn't Constantin who moves up in the higher title. In the emperor's conference of Carnutum Diocletian decides that Licinius will be the new Augustus of the West.

West ! East
Augusti Licinius Galerius
Caesares Constantin Maximinus Daia

5. Tetrarchy from May 311

After the death of Galerius he was succeeded by Maximinus Daia in the rank of an Augustus of the East, but is crowded by Licinius, who wants to have the status of the senior Augustus. Maximinus appoints firstly no new Caesar, although it was assumed, that this position should later on be filled out with the son of Severus, Flavius Severianus, or at least he was scheduled for this position.

West ! East
Augusti Licinius Maximinus Daia
Caesares Constantin vacant

(6.) Tetrarchy: after the 8. Octobre 316 to the end of 316

Shortly before the turn of the year 316/317 for a short-term exists the situation, that both Augusti Constantin and Licinius appoint again a Caesar. If both want to give the appearance of a continuity of the Tetrarchy is also unclear as the date stamping which could also be the turn of the year 314/315.

West ! East
Augusti Constantin Licinius
Caesares Bassianus Valerius Valens

(7.) Tetrarchy from 1. March 317 to 18. Septembre 324

The tetrarchic system is at its end, the dynastic system has won. Both Augusti appoint her own sons to co-emperors, Constantin even two of his sons. Short before of his end Licinius appoints the General Martinianus on 3. July 324 to his co-emeror.

West ! West East
Augusti Constantin Licinius
Caesares Crispus

Constantin 2. || Licinius 2.


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 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 until the fall of Rome's western empire left Byzantium, the "second Rome", sole direct heir).

Other examples

See also


  1. Historian David Potter translates the term as "gang of four". See idem., Constantine the Emperor (Oxford: Oxford University Press, 2013), 1.


  1. Qtd. and tr. Leadbetter, Galerius, 3.
  2. Leadbetter, Galerius, 3.
  3. Leadbetter, Galerius, 3–4.
  4. The chronology has been thoroughly established by Kolb, Diocletian, and Kuhoff, Diokletian.


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  • Kolb, Frank (1987). Diocletian und die Erste Tetrarchie. Improvisation oder Experiment in der Organisation monarchischer Herrschaft?, Berlin: de Gruyter. ISBN 978-3-11-010934-4
  • Kuhoff, Wolfgang (2001). Diokletian und die Epoche der Tetrarchie. Das römische Reich zwischen Krisenbewältigung und Neuaufbau (284–313 n. Chr.), Frankfurt am Main: Lang. ISBN 3-631-36792-9
  • Leadbetter, William Lewis (2009). Galerius and the Will of Diocletian. London and New York: Routledge.
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External links