Tetrarchy

• 1. System Origins And Design

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  Roman emperor Diocletian instituted a new system of governance in the late third century to address severe military and administrative crises. The Tetrarchy divided power among four rulers: two senior emperors called augusti and two junior colleagues known as caesares. This structure aimed to ensure that an emperor could personally command troops on multiple fronts simultaneously, solving a critical problem from the Third Century Crisis where leaders were often unable to be in more than one place at once. In 285, Diocletian chose Maximian as his caesar, raising him to co-augustus the following year. Maximian governed western provinces while Diocletian administered eastern ones. By March 293, Galerius and Constantius were appointed caesares under their respective augusti. The role of the augustus was likened to Jupiter, while his caesar was akin to Hercules. This orderly system endured until Constantius died in July 306, triggering a chain reaction of civil wars. The tetrarchic system lasted between AD 293 and 324, though its effective stability ended much earlier.

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• 2. Imperial Capitals And Regions

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  The four tetrarchs based themselves not at Rome but in other cities closer to the frontiers. These centers served as headquarters for defending the empire against bordering rivals like Sassanian Persia and barbarians along the Rhine and Danube rivers. Nicomedia in northwestern Asia Minor became the capital of Diocletian, the eastern augustus. Sirmium near Belgrade on the Danube border was the capital of Galerius. Mediolanum, modern Milan, served as the capital of Maximian, the western augustus. Augusta Treverorum, now Trier in Germany, was the capital of Constantius, the western caesar. Aquileia, a port on the Adriatic coast, and Eboracum, modern York in northern England, were also significant centers for Maximian and Constantius respectively. Although Rome ceased to be an operational capital, it remained the nominal capital of the entire Roman Empire under its own unique Prefect of the city. Each emperor had his zone of influence within the Roman Empire, mainly high command in a war theater rather than precise administrative division. The period did not see the Roman state actually split up into four distinct sub-empires. Each tetrarch was often in the field while delegating most administration to hierarchic bureaucracy headed by praetorian prefects.

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• 3. Propaganda And Public Image

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  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 numerous civil wars 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 Byzantine sculpture Portrait of the Four Tetrarchs shows the tetrarchs again with identical features and wearing the same military costume. Authority was recorded not only on coins and milestones but also on boundary stones from the Levant documenting local land surveys and village boundaries. Pliny the Elder once glossed the concept as each ruler being equivalent to a kingdom yet part of one. When later authors described the period, they emphasized that Diocletian's lesser colleagues spoke in unison under his command like a chorus surrounding a leader. Only Lactantius, a contemporary of Diocletian and deep ideological opponent, referred to the tetrarchs as a simple multiplicity of rulers. Modern scholarship did not use the term until Hermann Schiller used it in 1887 in a two-volume handbook on the Roman Empire.

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• 4. Military Campaigns And Victories

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  Under the Tetrarchy a number of important military victories were secured. After suffering a defeat by the Persians in 296, Galerius crushed Narseh in 298 reversing a series of Roman defeats throughout the century. He captured members of the imperial household and substantial amounts of booty gaining a highly favorable peace treaty securing peace between the two powers for a generation. Constantius defeated the British usurper Allectus while Maximian pacified the Gauls. Diocletian crushed the revolt of Domitianus in Egypt. Both the dyarchic and tetrarchic system ensured that an emperor was near to every crisis area to personally direct campaigns simultaneously on more than just one front. 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. Licinius was left in control of the east on the death of Maximinus Daza. The tetrarchic system lasted until circa 324 when mutually destructive civil wars eliminated most claimants to power. Licinius resigned as augustus after losing the Battle of Chrysopolis leaving Constantine in control of the entire empire.

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• 5. Dynastic Breakdown And Civil Wars

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  When Constantius died in July 306 his son Constantine was unilaterally acclaimed augustus and caesar by his father's army. Galerius instead chose to promote Severus to augustus while granting Constantine the position of caesar. At the same time Maxentius, the son of Maximian, resented being left out of new arrangements so he rebelled against and defeated Severus before forcing him to abdicate then arranging his murder in 307. Maxentius and Maximian both declared themselves augusti. By 308 there were therefore no fewer than four claimants to the rank of augustus and only one to that of caesar. In 308 Galerius together with retired emperor Diocletian and 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. This agreement proved disastrous: by 308 Maxentius had become de facto ruler of Italy and Africa even without any imperial status. Between 309 and 313 most 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.

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• 6. Administrative Legacy And Continuity

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  Although the tetrarchic system as such only lasted until 313 many aspects of it survived. The fourfold regional division of the empire continued in the form of Praetorian prefectures each overseen by a praetorian prefect and subdivided into administrative dioceses. These often reappeared in the title of military supra-provincial command assigned to a magister militum. The pre-existing notion of consortium imperii sharing imperial power and the idea that an associate to throne was designated successor reappeared repeatedly. The concept of two halves east and west re-emerged eventually resulting in permanent de facto division into two separate Roman empires after death of Theodosius I though Empire was never formally divided. Emperors of eastern and western halves legally ruled as one imperial college until Fall of Western Roman Empire left Byzantium second Rome as sole direct heir. In Eastern Roman Empire augusti and caesares continued to be appointed sporadically. 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 nephew Dalmatius in 335. Three surviving sons of Constantine in 337 were declared joint augusti together while concept of division under multiple joint emperors endured until Fall of Western Roman Empire.

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