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Gaius Aurelius Valerius Diocletianus (245-313 AD/CE), born Diocles, was Roman Emperor from November 20, 284 to May 1, 305. Diocletian brought to an end the period known as the "Crisis of the Third Century (235-284). He established an autocratic government and was responsible for laying the groundwork for the second phase of the Roman Empire, which is known variously as the "Dominate," the "Tetrarchy," the "Later Roman Empire," or the "Byzantine Empire". His reforms ensured the survival of the Roman Empire, in the east, for more than a thousand years.

Emperor Diocletian on a period coin
Emperor Diocletian on a period coin

An Illyrian of low birth (from the province of Dalmatia), Diocles rose through the ranks to the consulship. He was chosen by the Army on November 20, 284 to replace Numerian and after the assassination of Carinus in July, 285 became sole ruler of the Roman Empire. He changed his name to Diocletian upon his ascension.

Prior to Diocletian becoming Emperor, between 235 and 284 there were roughly 20 to 25 different Emperors in a period of about 50 years, or on average a new Emperor every 2 to 3 years. In 284 an element within the Roman army proclaimed general Diocletian to be Emperor. Between 284 and 298 Diocletian seemed to be following in the footsteps of his short-lived predecessors as he fought a long string of wars from one end of the Roman empire to the other, racing back and forth maintaining the boundaries of the frontiers and stamping out uprisings at home. However by 298 he had succeeded in removing Germanic intrusions from across the Danube and Rhine, put a halt of Persian invasions in Syria and Palestine, and defeated his rivals within the Empire.

With his position secure, a remarkable feat after over 50 years of internal instability that nearly saw the collapse of the Roman Empire (what has become known as the Crisis of the Third Century), he believed going forward the system of Roman imperial government was unsustainable. Diocletian began a number of reforms and changes to prevent a return to the anarchy of previous generations and maintain the viability of the Empire. These included splitting the Empire in two to be more manageable; creating a new system of Emperor succession; ruling as an autocrat and stripping away any remaining facade of republicanism; and economic reforms to address the problem of hyperinflation.

Diocletian chose a new title for himself, calling himself Dominus et deus, or "Lord and God". This was in contrast to previous Emperors, who were known as Princeps or "First Citizens", a name which implied some level of equality and democracy, even if in name only. Diocletian through his new title removed any such facade, installing himself as a supreme overlord. He was not to be seen in public, and if an audience was required, he had elaborate ceremonies in which the visitor would be required to lay on the ground prostrate and never to look at the Emperor, allowed perhaps to kiss the bottom of his robe. In this way he created a remote, mysterious and autocratic office of Emperor.

Diocletian's experiences during his first nine years of running around the Empire putting out fires brought him to the conclusion that the Empire was simply too big for a single Emperor to rule—that it was not feasible to address barbarian invasions along the Rhine and Egyptian problems at the same time, for example. His radical solution was to split the Empire in two, drawing a line straight down the middle of the map with the axis just east of Rome into eastern and western halves. While this division did not last in the short term, it did eventually become permanent.

The question of Emperor succession had never been solved in the Roman system; there was no clear principal of succession, which often led to civil wars. Prior Emperors had preferred the system of adoption, whereby they would adopt a son in order to be the chosen heir. The military did not like the system of adoption and preferred biological succession, with the emperors son being the rightful heir. The Senate believed they should have the right to elect a new Emperor. Thus there were usually at least three, if not many more, rightful heirs of succession.

In order to solve the problem of succession, and to answer the question of who would be Emperor of the new divided east and west, Diocletian created what has become known as the system of "Tetrarchy", or "rule of four", whereby a senior emperor would rule in the east and west, and each would have a junior emperor known as a Caesar. When the senior emperor (known as an Augustus) retired or died, the Caesar would take his place and choose a new junior emperor Caesar to take his place, thus solving the problem of succession.

By 292 Diocletian had the system in place and chose the eastern empire for himself and gave Maximian the western empire. The imperial power was now divided between two people. Diocletian's sphere of influence was the east, and Maximian's the west. The two men established separate capitals, neither of which was at Rome. The ancient capital was too far removed from the places where the empire's fate was decided by force of arms. While improving the ability of the two emperors to rule the empire, the division of power further marginalized the Senate, which remained in Rome. In 292, Diocletian and Maximian each appointed a Caesar (Galerius and Constantius, respectively). However, these were not merely successors - each was given authority over roughly a quarter of the empire.

Considering that during the half-century preceding Diocletian's ascension the empire had been in a constant state of simmering civil war it is remarkable that the Tetrarchy did not immediately fall apart due to the greed of any one of the four emperors. However the opportunistic nature of Roman imperial politics soon caused the disintegration of the Tetrarchy and the reinstitution of one-man rule. When in 305 Diocletian retired (and his western counterpart was convinced to do the same), the two Ceasers became the senior emperors as designed, but when it came time to choose new Ceasers, the military and Senate intervened and brought forward their own canidates. In 306 Constantine began a civil war in the west, which he won in 312, and took the eastern half by 324, thus ruling as a united Empire until his death in 337. However by 395 the division occurred again and the two halves would never be united again.

Economically Diocletian made reforms. In 301, Diocletian attempted to curb the rampant inflation of the 3rd century, and issued his Edict on Maximum Prices. This Edict fixed prices for over a thousand goods, fixed wages, and threatened the death penalty to merchants who overcharged. It was unable to stop the inflation and was eventually ignored, but it is an important document for an understanding of Roman economics.

In 303, the last and greatest persecution of Christians by the Roman Empire began, although Galerius carried it out more avidly than Diocletian himself. This wave of persecution lasted until 311.

In 305 at the age of 59, after almost dying from a sickness, Diocletian retired to his palace near the administrative center of Salona on the Adriatic Sea, taking up his beloved hobby of growing cabbages. When solicited at a later date to resume the honours which he had voluntarily resigned, his reply was, "Would you could see the vegetables planted by my hands at Salona, you would then never think of urging such an attempt." He was the only Roman emperor to remove himself from office; all of the others either died of natural causes or were removed by force.

Diocletian's Palace later became the seed of modern Split, Croatia.

Dioceses of Diocletian

Name Territories
Oriens Libya, Egypt, Palestine, Syria, and Cilicia
Pontus Cappadocia, Armenia Minor, Galatia, Bithynia
Asia (Asiana) Asia, Phrygia, Pisidia, Lycia, Lydia, Caria
Thrace Moesiae Moesia Inferior, Thrace
Moesia Moesia Superior, Dacia, Epirus, Macedonia, Thessaly,

Achaea, Dardania

Africa Africa Proconsularis , Byzacena, Tripolitana , Numidia, part of


Hispania Mauretania Tingitana, Baetica, Lusitania,


Prov. Viennensis Narbonensis, Aquitania, Viennensis, Alpes


Gallia Lugdunensis, Germania Superior, Germania

Inferior, Belgica

Britannia Britannia, Caesariensis
Italia Liguria, Venetia, Alpes Cottiae,

Alpes Graiae, Raetia

Pannonia Pannonia Inferior, Pannonia Superior, Noricum,


Suburbicaria Umbria, Campania, Sicilia, Corsica, Sardinia

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Last updated: 10-18-2005 12:51:36
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