Tetrarchy
The Tetrarchy was the system instituted by Roman emperor Diocletian to govern the ancient Roman Empire by dividing it between two emperors, the augusti, and their junior colleagues and designated successors, the caesares. It was kept in place between AD 293 and 324.
Initially Diocletian chose Maximian as his caesar in 285, raising him to co-augustus the following year; Maximian was to govern the western provinces and Diocletian would administer the eastern ones. The role of the augustus was likened to Jupiter, while his caesar was akin to Jupiter's son Hercules. Galerius and Constantius were appointed caesares in March 293. Diocletian and Maximian retired on 1 May 305, raising Galerius and Constantius to the rank of augustus. Their places as caesares were in turn taken by Valerius Severus and Maximinus Daza.
The orderly system of two senior and two junior rulers endured until Constantius died in July 306, and his son Constantine was unilaterally acclaimed augustus and caesar by his father's army. Maximian's son Maxentius contested Severus' title, styled himself princeps invictus, and was appointed caesar by his retired father in 306. Severus surrendered to Maximian and Maxentius in 307. Maxentius and Constantine were both recognized as augusti by Maximian that same year. Galerius appointed Licinius augustus for the west in 308 and elevated Maximinus Daza to augustus in 310.
Constantine's victory over Maxentius at the Battle of the Milvian Bridge in 312 left him in control of the western part of the empire, while Licinius was left in control of the east on the death of Maximinus Daza. Constantine and Licinius jointly recognized their sons – Crispus, Constantine II, and Licinius II – as caesares in March 317. Ultimately the tetrarchic system lasted until c. 324, when mutually destructive civil wars eliminated most of the claimants to power: Licinius resigned as augustus after losing the Battle of Chrysopolis, leaving Constantine in control of the entire empire.
The Constantinian dynasty's emperors retained some aspects of collegiate rule; Constantine appointed his son Constantius II as another caesar in 324, followed by Constans in 333 and his nephew Dalmatius in 335, and the three surviving sons of Constantine in 337 were declared joint augusti together, while the concept of the division of the empire under multiple joint emperors endured until the Fall of the Western Roman Empire. In the Eastern Roman Empire, augusti and caesares continued to be appointed sporadically.
Terminology
The term tetrarchy describes any form of government where power is divided among four individuals.Although the term "tetrarch" was current in antiquity, it was never used in 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".
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 Gallus for disobedience by appealing to the example in submission set by Diocletian's lesser colleagues; his successor Julian 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.
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, to wit: "die diokletianische Tetrarchie". Even so, the term did not catch on in the literature until Otto Seeck used it in 1897.
File:Argenteus-Constantius I-antioch RIC 033a.jpg|thumb|On the reverse of this argenteus struck in Antioch under Constantius I, the tetrarchs offer sacrifice to celebrate a victory against the Sarmatians.
Creation
The first phase, sometimes referred to as the diarchy, involved the designation of the general Maximian as co-emperor—firstly as caesar 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, Diocletian thought that more focus was needed on both civic and military problems, so with Maximian's consent, he expanded the imperial college by appointing two caesares —Galerius and Constantius I.In 305, the senior emperors jointly abdicated and retired, allowing Constantius and Galerius to be elevated in rank to augustus. They in turn appointed two new caesares—Severus II in the west under Constantius, and Maximinus in the east under Galerius—thereby creating the second Tetrarchy.
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 and barbarians 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.The four tetrarchic capitals were:
- Nicomedia in northwestern Asia Minor, a base for defence against invasion from the Balkans and Persia's Sassanids was the capital of Diocletian, the eastern 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 praetorian prefecture Oriens, 'the East', the core of later Byzantium.
- Sirmium was the capital of Galerius, the eastern caesar; this was to become the Balkans-Danube prefecture Illyricum.
- Mediolanum was the capital of Maximian, the western augustus; his domain became "Italia et Africa", with only a short exterior border.
- Augusta Treverorum was the capital of Constantius, the western caesar, near the strategic Rhine border; it had been the capital of Gallic emperor Tetricus I. This quarter became the prefecture Galliae.
In terms of regional jurisdiction there was no precise division among 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 theater'. Each tetrarch was himself often in the field, while delegating most of the administration to the hierarchic bureaucracy headed by his respective praetorian 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, 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.
The Tetrarchs’ authority is recorded not only on coins and milestones but also on boundary stones from the Levant, which document local land surveys and village boundaries.
Public image
Although power was shared in the tetrarchic system, the public image of the four members of the imperial college was carefully managed to give the appearance of a united empire. This was especially important after the numerous civil wars 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 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. 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 near 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.