The Tetrarchy from Diocletian to Constantine: Emperors of Rome

Emperor Diocletian decided to retire in April 305, assuming that the system for sharing imperial authority that he had set up would continue along the same lines. However, things did not run as smoothly as he had hoped.

Diocletian had split the empire into twelve “dioceses”, with each of four “tetrarchs” running three of them apiece. He and Maximian were the two senior tetrarchs, with Constantius and Galerius being subservient to them. Diocletian’s plan was for Maximian and himself to retire at the same time, with Constantius and Galerius moving up to fill the senior positions (“Augusti”) and two new men being appointed to be junior emperors (“Caesares”).

The original thought had been that the sons of Constantius and Maximian, namely Constantine and Maxentius respectively, would be the new Caesars, but Diocletian changed his mind on this. He subsequently announced that the new junior emperors-in-waiting would be a general named Flavius Valerius Severus and Maximinus Daia, who was a nephew of Galerius.

The problem was that not all the new men who took office on 1^st May 305 were content with what Diocletian had decreed. In particular, Constantius was annoyed that his son Constantine had been excluded from the succession.

It was not long before this source of dissent turned from being a potential problem to an actual one. Constantius was responsible for Britain and it was while he was in Britain in July 306 that he died at Eboracum (York). The army, presumably following the expressed wish of Constantius, declared Constantine to be the new emperor.

Meanwhile Maxentius, who was the other man to lose out when Diocletian changed his mind about the succession, refused to let matters lie and claimed the position that Diocletian had assigned to Severus. His father Maximian gave him his support, which was essential in deciding the issue because the army, which had served under Maximian, refused to back Severus who was imprisoned and eventually killed.

In 307 Galerius invaded Italy, hoping to defeat Maxentius and restore the arrangement that Diocletian had decreed. Constantine refused to take sides and Rome, protected by the walls erected 30 years previously by Aurelian and Probus, proved to be capable of withstanding a siege. Galerius had no choice but to withdraw.

On the other hand, Galerius did have a powerful friend to call upon for help, namely Diocletian who was quietly growing cabbages on his estate at Split (in modern Croatia). A conference was called in 308 at Carnuntum (in modern Austria), under the chairmanship of Diocletian, at which it was agreed that Constantine could continue to rule the regions he already controlled and Galerius would continue as the other senior emperor. A new junior emperor was appointed to replace Severus, this being a general named Licinius.

With civil war avoided, Diocletian went back to his vegetables and Galerius was happy to be recognized as the most powerful person in the empire. Unfortunately for him, he only lived to enjoy this status for another three years, dying of natural causes (a very nasty case of bowel cancer) in May 311.

The surviving emperors, who now all regarded themselves as Augusti rather than Caesares, then divided into two factions, Maximinus allying himself with Maxentius and Constantine with Licinius. One result of Diocletian’s reforms had been that the army, as well as the government, had split into what were virtually independent camps that were loyal to one or other of the tetrarchs. The result was that each of the four men controlled roughly equal forces, so any power struggle was likely to result in a highly destructive civil war.

In the event, the struggle boiled down to a contest between Constantine and Maxentius. Constantine was a strange character who exhibited a range of personality traits, one of which was a deep belief in divine intervention. The question was, which god to trust? He had long been a devotee of Sol Invictus – also known as Elagabal, the Syrian sun god who had originally been introduced to Rome by Elagabalus and then re-introduced by Aurelian. Constantine now decided to place his trust in the Christian god.

The story of Constantine’s conversion has become a legend, not least because of the profound implication it would have for the growth of Christianity as well as the later history of the Roman Empire. The truth of what happened is less easy to ascertain. However, the fact remains that Constantine was able to defeat Maxentius, and he ascribed his victory to what he termed the “Divine Mind”.

After the final battle with Maxentius at the Milvian Bridge on 28^th October 313, at which Maxentius was killed, Constantine was clearly the most dominant figure in Roman politics, and the Tetrarchy, such as it now was, was no longer a government by equal parties. 

© John Welford

Diocletian, Emperor of Rome

Diocletian was one of the more effective later Roman Emperors and also had the distinction of being the only Emperor to abdicate his throne voluntarily.

Gaius Aurelius Valerius Diocletianus was born in Dalmatia, probably in 245, of obscure parentage. He had a career in the army under Emperors Aurelian, Probus and Carus, and was on campaign with Carus in Mesopotamia in 283 when the latter died suddenly. Legend has it that his tent was struck by lightning, but this could be taken as meaning that he was murdered by mutineers.

Carus had two sons, Carinus and Numerian, the latter of whom was on campaign with him while Carinus remained at home. Numerian was murdered in the summer of 284, but his assassins had no idea what to do next and pretended that their victim was still alive but suffering from an eye infection that prevented him from appearing in public. Eventually the stench from the rotting corpse became too powerful to ignore and the senior officers realised that they had to choose a compromise candidate for Emperor to set against Carinus.

The choice fell upon a mid-ranking officer called Gaius Aurelius Valerius Diocles who took the name Diocletianus that is commonly abbreviated to Diocletian. His first act as Emperor was to take his sword and kill the praetorian prefect Flavius Aper whom he accused of the murder of Numerian.

In 285 the forces of Diocletian and Carinus met in battle at the Margus River in Moesia (modern Serbia). The battle was going in favour of Carinus when some of his troops mutinied and he was probably murdered by someone on his own side. Diocletian was now undisputed as Emperor.

Despite being unchallenged, Diocletian was wise enough to realise that things were unlikely to stay that way. Past history showed that, with Emperors having to be constantly on the move to defend the frontiers at one point or another, the close relationship between the governing class in Rome and the Emperor’s inner circle was breaking down. Without this communication there was every chance of factions arising that would foment rebellion and civil war. It was impossible to have a mobile Emperor and stable central authority at the same time.

Diocletian therefore took steps to devolve his authority by sharing power on a regional basis. He married one of his daughters to an officer called Maximian who was then made Augustus with dominion over the western provinces of the Empire, although it was made clear that Diocletian, in the east, would have seniority over him. Two junior Emperors, with the rank of Caesar, were also appointed later on, these being Flavius Constantius and Gaius Galerius. Constantius acted as deputy to Maximian and Galerius worked with Diocletian. The juniors also established a family relationship with their bosses by marrying their daughters. This four-way arrangement is known to historians as the Tetrarchy.

Diocletian also established new power bases for the Empire, with the emphasis being taken away from Rome itself. He established himself at Nicomedia in northwestern Turkey, and only visited Rome twice during his 21 years as Emperor. Other centres were where the Emperor, junior or senior, chose to reside, with palaces being built at Sirmium (Serbia), Aquileia and Milan (northern Italy), and Trier in Germany.

Diocletian went further by subdividing local government into twelve “dioceses”, equally divided between the eastern and western halves of the Empire. Although these enabled power to be devolved away from Rome, they increased the overall bureaucratic burden of running the Empire and also had the long-term effect of weakening its overall cohesion.

Another reform was to create a civil adminstration that was no longer dominated by the super-rich. This had been made easier by the hyperinflation of previous reigns, so that the huge fortunes of those at the top were now worth much less, and property valuations that had previously defined the class structure were now meaningless. It was therefore possible for people of relatively modest means to gain high office.

Reforms were also made to the legal and taxation systems, and Diocletian tried to institute economic stability through an “Edict on Maximum Prices”, although this proved to be a failure because it ignored some of the basic laws of supply and demand.

Despite his well-deserved reputation for clemency and humanity, Diocletian was not above persecuting Christians. In February 303 he issued an Empire-wide edict that ordered all Christians to sacrifice to the traditional gods, with severe punishments threatened for those who disobeyed. However, the tetrachs differed in their application of the edict, which ceased to be enforced after about 18 months. It was in any case becoming very difficult to enforce such edicts in a world where Christians had infiltrated institutions including the army, the imperial court and higher education.

In 305, having reached the age of 60, Diocletian decided to retire. His plan was that he and Maximian would retire at the same time, leaving the junior emperors to step into their shoes and appointing two new men as Caesars (Maximinus Daia and Flavius Valerius Severus). Maximian was not overjoyed at the idea, but he had no choice. At a ceremony on 1st May the two senior emperors abdicated.

Diocletian retired to a palace in his native Dalmatia where he enjoyed his later years growing vegetables in his garden, but he was to be called upon again to settle the power balance of the Empire.

Diocletian’s legacy should have been a degree of stability that the Empire had not known for a long time. However, despite the apparent elements of devolution, the arrangements under the Tetrarchy still depended on each member conceding that the ultimate decision-making power lay with one man. Once that man had gone, it was open season again for ambitious men to grab as much power as they could.

Galerius found that he did not have the authority of Diocletian to assert himself over other claimants, notably Maxentius who was the son of Maximian, who in July 306 came out of retirement to support his son’s claim to be Emperor after Constantius’s son, Constantine, had been declared Emperor on the death of his father. Galerius called on Diocletian to come to his aid.

Diocletian presided over a conference at which Galerius ended up being recognised by all parties as the senior Emperor. However, there was no guarantee that future trouble of a similar kind could be avoided without bloodshed, and this was indeed what was in store in later years.

Diocletian died in 313 (this is not certain, it could have been earlier) at the age (probably) of 68.

© John Welford

Diocletian's persecution of the Christians

23^rd February 303 was the day on which Diocletian, Emperor of Rome, declared the beginning of one of the worst episodes of persecution of the growing sect known as Christians.

Diocletian governed a vast empire that stretched across much of northern Europe, including southern Britain, and right round the Mediterranean Sea. In order to maintain the stability of the Empire, which incorporated many different nationalities, it was essential for all its subjects to recognise the supremacy of its central figure, namely the Emperor.

Diocletian took this necessity to the extreme of declaring himself to be a living god who must therefore be worshipped. This was something of a Roman tradition, so he was not doing anything new. However, what he could not tolerate was the existence within his empire of people who did not accept this state of affairs. If they worshipped a different god they were not part of a united empire and were therefore likely to cause disruption to the overall “pax Romana” (Roman peace).

Diocletian’s persecution was therefore based on political rather than religious motives. It did not help that the Christians were also given to arguing among themselves, which was therefore a potent cause of public disorder. Christians were also in the habit of condemning the lax morals of non-Christians, which caused much resentment. By suppressing Christians of all persuasions, Diocletian therefore hoped to remove a source of potential conflict.

The first order given was to destroy all Christian churches throughout the Empire. This led to resistance from Christians, and governors of Roman provinces countered this opposition with increasing degrees of severity. Although Diocletian had not originally envisaged the wholesale slaughter of Christians, this became inevitable when other forms of suppression proved ineffective.

Later edicts proposed harsher punishments for refusal to worship the Emperor, and local governors became highly imaginative in their methods of torturing and executing Christians. Many saints in the Christian calendar were victims of the Diocletian persecution, being done to death in particularly horrific ways.

Horrible though it was, the period of persecution did not last long. Diocletian retired from office in the year 305 and within a few years the emperor was Constantine, who famously became a Christian himself as did nearly all his successors.

© John Welford