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Diocletian and the Tetrarchy

Andrew is an avid reader who enjoys researching and discussing history with others.

The Ascension of Diocletian

On November 20, 284, an officer of the Roman Imperial army named Diocles was saluted by the army as the new emperor of the Empire. Diocles drew his sword and killed the Praetorian Prefect named Aper in full view of the army. Diocles held Aper responsible for the death of the previous emperor Numerian. Though nobody witnessed the demise of Numerian, the fact that Aper concealed the emperor’s death convinced the army that he was involved in Numerian’s death and nobody lifted a finger to save Aper when Diocles executed him.

The sudden rise and fall of emperors became an all too familiar feature of the 3rd century Roman Empire. During the period between 235 and 284, known as the Third Century Crisis, more than thirty emperors ruled over the Roman Empire, and every of these died of natural causes. Quite contrary, the position of the emperor was as good as a drawn-out death sentence.

Yet, Diocles had no intention of following his predecessors’ example and fell victim to the dagger of his own soldiers.

After his ascension, he changed his name to the more Latin-sounding Diocletian and implemented reforms throughout the empire that finally brought an end to the Third Century Crisis and brought back a measure of stability to Rome.


For each question, choose the best answer. The answer key is below.

  1. Before he rose to power what profession did Diocletian pursue?
    • High ranking soldier
    • Civilian administrator

Answer Key

  1. High ranking soldier

Elavation of Maximian

After defeating the older brother of Numerian, Carinus, at the Battle of Margus, Diocletian became the sole emperor of the Roman Empire. He went to Italy to consolidate his regime and succeeded in winning over to his cause the elites of Rome. When Diocletian entered Rome is still a matter of debate, and it is also not exactly known how much time he spent in the Eternal City, but by late 285, he was back in the Balkans and was fighting against the Sarmatians.

Diocletian did not clear out the officers and leading administrators of his predecessor Carinus. Some historians believe the sole reason for this clemency was that these had defected over to Diocletian during the Civil War against Carinus.

Diocletianic propaganda portrayed Carinus as one of the worst emperors of Rome’s history, a debauched, cruel womaniser who seduced his officers’ wives. Whether it is true or not is difficult to know, as the history of Carinus was written by the man who defeated him and had every reason to blacken the memory of his adversary.

In a rather surprising fashion, not long after he consolidated his rule, Diocletian named one of his trusted officers, Maximian, as co-emperor and raised him to the purple. Though it might have seemed like an illogical move, in reality, it was a wise move by Diocletian.

One reason (if not the main) that so many usurpers emerged during the Third Century was the constant multi-pronged attacks on the empire’s extended borders from many directions. The emperor’s more often than not led their troops in person, but no matter how capable that emperor was, he could only be in one place at a single time.

This led to the necessity to delegate conflict zones to his subordinates, who often became rebels. He used this force and the military glory they had acquired by defeating the attacking barbarians to launch his own bid for the purple.

Diocletian knew fully well that this situation wasn’t going to change in his rule either, so by elevating a trusted officer as his co-emperor, he no doubt hoped to preempt usurpations.


For each question, choose the best answer. The answer key is below.

  1. How long did Diocletian rule for?
    • 30 years
    • 20 years
    • 25 years

Answer Key

  1. 20 years

Other Reforms

Several years after the elevation of Maximian as co-emperor, Diocletian elevated two other of their subordinates as junior emperors. This scheme was enacted to solve Rome’s succession problems throughout its Imperial period. Despite the charade of a civilian authority still existent in the empire, in reality, the Roman Empire was a military dictatorship, and the emperors knew this perfectly well.

Septimius Severus advised his sons to keep the army paid and fed, the safest protection for their rule. Some emperors nominated their sons as their successors, while other childless emperors chose some trusted subordinates to follow them after their death. This latter method was by far the better one, as the sons of the former emperors often turned out to be rather incompetent and sometimes not much more than mere children.

Diocletian’s method would have carved up the empire into four parts. Four emperors ruled the different domains of the empire. There were two senior emperors (Augustus), one in the east and one in the west, and two juniors emperors(Caesar), one in the east and one in the west. Upon the abdication of the two Augustus, the Caesars became the senior emperors, and they chose their own junior emperors, who would have followed them upon their abdication.

It was a clever idea; unfortunately, it only worked while Diocletian was in power to enforce it. When Maximian was not followed by his son Maxentius, the ambitious Maxentius rose to power anyway, thanks to the support of his father’s soldiers. When Constantius died in Britain, his soldiers also elected his son Constantine rather than somebody else.

The Reforms of Diocletian

Diving power among trusted men and solving the succession issue was not the only way Diocletian had to pre-empt usurpations. Before his rule, the empire was divided into rather large provinces.

The governors of the provinces were the senior military and civilian administrators. This had left the governors, who usually were a member of some important senatorial family, with a considerable armed force, which in theory could have been used to march against the emperor also.

Diocletian had no interest in maintaining this status quo and decided to break the provinces into smaller subunits. Many emperors (4) made it possible for an emperor to be ever-present in the frontier region if the need arose. For similar reasons, the military and civilian powers were divided up in the provinces, and no single person could hold onto both.

A final measure of safety for the emperors was that from the time of Diocletian onwards, the emperor became much more secluded from the outside world than they were before. Augustus, for example, very much liked to appear among his people. Caesar and Sulla were known for walking among the people even without a bodyguard; in the case of Sulla, it was believed that he even explained his actions to citizens who questioned him.

Though the later emperors were nowhere near as open and easy to access as the before mentioned examples, they were still not oriental type secluded despots, like what the emperor’s often were from the times of Diocletian onwards.

Diocletian’s reign undoubtedly greatly stabilised the empire, but this stability had its price. Under Diocletian’s rule, the taxation system of the empire became much more efficient than it was under his predecessors, which in reality meant that the percentage of wealth that ordinary citizens were able to keep dwindled.

Diocletian used this revenue to build a much-enlarged administration for the empire. His new bureaucracy dwarfed the previous one when the local elites were left in peace so long as they paid the taxes the empire required of them.

Peasants, Soldiers and Town Councillors

Many of the free peasants also no doubt cursed Diocletian and his successors. The free farmers, known as colonii, became tied to their lands. Some historians, for this reason, date the beginning of serfdom from the rule of Diocletian.

Peasants were not the only category disadvantaged by Diocletians’ laws either. Many historians believe that during the reign of Diocletian and his successors, the size of the imperial army was greatly expanded, and the only method to fill the ranks of the expanded army was conscription and hiring barbarians.

As the Roman economy was based on agriculture, hiring many peasants as soldiers on a permanent base was impossible. These people had to work the fields and grow food for the cities and the army. However, the sons of the soldiers were a category that could be used to make up the numbers, and this is exactly what happened.

The sons of soldiers were not the only ones under a legal obligation to follow in their father’s footsteps either. After the growth of the Imperial bureaucracy, the local elites ditched their positions in the town councils to pursue a career in the imperial administration. This phenomenon often left the town councils lacking in numbers, which in turn led to badly managed towns.

To stop the local elites from ditching these positions, Diocletian made it a legal obligation for the sons of town councillors to occupy their father’s positions, making the positions as good as hereditary. Once again, a very medievalesque development, when as we all know, oftentimes cities were run by traditional oligarchic families.


Goldsworthy, Adrian. (2010). How Rome Fell: Death of a Superpower. Yale UP.

Heather, Peter. (2006). The Fall of the Roman Empire: A New History. Pan Books.

Southern, Pat. (2001). The Roman Empire from Severus to Constantine. Routledge.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2022 Andrew Szekler