Emperor Diocletian

Podcast Transcript

In the middle of the Third Century, things were looking really bad for the Roman Empire.

This period was marked by civil war, economic collapse, foreign invasions, and a rapid succession of emperors, often military usurpers, most of whom died violently.

If things had gone just a little differently, we would have been talking about the collapse of the Roman Empire centuries before it finally did.

It didn’t collapse because of one man who radically changed the way the empire was run.

Learn more about Emperor Diocletian and how he stopped the decline of Rome on this episode of Everything Everywhere Daily.

Depending on how you count, there were approximately 70 to 80 individuals, including co-emperors, usurpers who ruled significant territory, and short-lived rulers, who could be considered Roman Emperors prior to the fall of the Western Empire over a period of about 500 years.

The men who held the position were a very mixed bag.

You had literal children, old men, soldiers, philosophers, hedonists, geniuses, and psychopaths.

The standard by which historians have considered some emperors to be great has more to do with the stability they brought to the empire than their personal ability.

Most lists of the “greatest” Roman Emperors usually include Diocletian.

That doesn’t mean Diocletian was a great guy—more on that in a bit—but rather that his accomplishments as Emperor helped preserve and protect the empire and provided stability and peace.

To understand the importance of Diocletian, we need to understand the mess that the empire was in before he rose to power.

The empire experienced fifty years of what historians have called the Crisis of the Third Century, a subject I covered in a previous episode.

The Crisis of the Third Century, which lasted from 235 to 284, was a period of profound turmoil and near collapse for the Roman Empire. It began with the assassination of Emperor Alexander Severus and was marked by constant civil war, with over twenty emperors rising and falling in rapid succession, often through military coups.

The empire faced severe external pressures, including invasions by Germanic tribes and Persian armies, while internal divisions led to the temporary secession of regions like the Gallic and Palmyrene Empires. Economic instability, rampant inflation, and a breakdown in trade further weakened the state, and a series of plagues decimated the population.

The empire teetered on the edge of disintegration until the rise of Diocletian in 284, who restructured the imperial system and helped restore order.

Diocletian was born Gaius Valerius Diocles around 244 in the Roman province of Dalmatia in modern-day Croatia.

Little is known about Diocletian’s early life. He came from a non-aristocratic background, possibly of Illyrian descent, and joined the Roman army, where he rose through the ranks due to his competence and loyalty. By the 280s, he had become a commander in the imperial bodyguard under Emperor Carus.

After the sudden deaths of Carus and his son Numerian in 284, Diocletian was proclaimed emperor by the army. He cemented his position by defeating Carus’s surviving son, Carinus, at the Battle of the Margus in 285, in present-day Serbia, after which he became the uncontested ruler of the Roman Empire.

This was quite an accomplishment, but what he inherited was a mess and something that over a dozen men had claimed over the last 50 years, which resulted in most of their deaths by assassination.

One of the first problems that Diocletian addressed was the issue of the size of the empire and imperial overstretch. One person simply couldn’t govern a territory that large, especially in an era when information had to travel by ship or horseback.

There had also been a problem since the days of Augustus, when imperial succession was never clear. In most cases, there was no set system in place to determine who the next emperor would be. This often led to wars and usurpers who felt that they could claim the throne via force.

Diocletian tried to solve both of these problems by establishing a system called the Tetrarchy in 293, which in Latin meant the rule of four.

Under this system, the empire would be split into two administrative halves, the east and the west.

Each half of the empire would be ruled by a senior emperor who would be known as an Augustus. These men would be co-emperors.

Alongside each Augustus would be a junior emperor who held the title of Caesar. The junior emperor would be learning on the job the duties of administering the empire and, in theory, would take over for the senior emperor.

Diocletian appointed a military leader named Maximian as his co-emperor and the Augustus in the West, while he governed the East.

Each Augustus then appointed a subordinate Caesar—Constantius Chlorus under Maximian, and Galerius under Diocletian.

While the empire was effectively still a single entity, it was the start of the formal division between East and West, which would eventually result in what we know as the Byzantine Empire centuries later.

This division required Diocletian to voluntarily give up some of his power, which was unprecedented. There were co-emperors in the past, but it was always with family members such as brothers or fathers and sons.

Diocletian also restructured Roman provincial administration.

He doubled the number of provinces, from around 50 to nearly 100, making them smaller and more manageable.

He then grouped provinces into 12 larger dioceses, each under an administrator called a vicarius.

He separated military and civilian authority, reducing the risk of powerful governors leading rebellions.

He also expanded the imperial bureaucracy significantly, creating a more complex but effective administrative system to govern a large empire.

Diocletian’s economic reforms were among the most ambitious attempts in Roman history to address the deep-seated financial and structural problems that had developed during the Crisis of the Third Century.

When Diocletian came to power, the Roman Empire was suffering from hyperinflation, declining productivity, a collapsing currency, and inconsistent tax collection. His reforms, though not entirely successful in practice, represented a fundamental shift in how the Roman economy was administered.

One of the most urgent issues Diocletian faced was currency debasement. For decades, emperors had reduced the silver content in coins to stretch imperial resources, resulting in rampant inflation and the public’s loss of confidence in money. Diocletian attempted to restore monetary stability by issuing a new coinage system.

He introduced the aureus, a high-purity gold coin, intended for large transactions and the military. He also introduced a new silver coin, the argenteus, with a consistent weight and silver content.

New bronze and copper coins were also created to replace the largely worthless older coinage.

In 301, Diocletian issued the Edict on Maximum Prices, one of the most famous and far-reaching aspects of his economic policy. This decree attempted to curb inflation by setting maximum prices for over a thousand goods and services, including food, clothing, labor, and transportation. The edict also imposed harsh penalties—including death—for those who violated its terms.

The intention was to prevent price gouging and protect consumers from market manipulation, especially during times of scarcity. However, it backfired in practice. Prices were set unrealistically low, leading to shortages, the disappearance of goods from markets, and the emergence of black markets. The law was widely ignored and eventually abandoned, though it survives in inscriptions as a testament to the severity of the economic crisis.

Another critical element of Diocletian’s reforms was the overhaul of the taxation system, which had become chaotic and arbitrary during the crisis years. To make tax collection more efficient and fair, Diocletian restructured it around a system called the capitatio-iugatio.

The Capitatio was a tax on individuals, based on the number of working people (especially peasants) in a household.

The Iugatio was a land tax, based on the size, fertility, and productivity of land holdings.

Together, these were calculated in fiscal units tied to both land and labor productivity, aiming to create a more equitable and predictable tax burden.

This system required a more accurate and regular census, which Diocletian mandated to be taken every 5 years. The result was a more rigid system in which peasants and landowners were closely tied to their tax obligations.

To ensure tax collection and maintain agricultural production, Diocletian took steps that effectively bound people to their social and economic roles. Tenants on agricultural estates were prohibited from leaving the land, which laid the foundation for the later system of serfdom. Similar constraints were placed on workers in key industries, such as shipbuilders, bakers, and armorers, making their professions hereditary.

If your father was a barber, then you had to be a barber. It completely eliminated social and economic mobility in the empire.

This was part of a broader shift toward a command economy, where the state sought greater control over economic life. By fixing people in place, Diocletian hoped to ensure a stable tax base and reliable provisioning for the military and the urban population.

Overall, his monetary reforms were much needed, but his other reforms ultimately caused more harm than good.

The other major policy that he is best known for was his treatment of Christians.

Though he initially tolerated Christianity, Diocletian came to view it as a threat to imperial unity. In 303, under the influence of Galerius and traditional Roman religious advisors, Diocletian launched the Great Persecution, the most severe and systematic effort to suppress Christianity in Roman history.

Churches were destroyed, scriptures burned, and thousands of Christians were imprisoned or executed. While the persecution varied in intensity across the empire, it ultimately failed to eradicate Christianity.

Perhaps the most profound change he made was that he completely changed the nature of being Emperor.

Diocletian transformed the Roman system of imperial governance from the Principate, established by Augustus, into the Dominate, a more autocratic and centralized regime.

Under the Principate, the emperor styled himself as princeps (“first citizen”), maintaining the illusion that he ruled in cooperation with the Senate and within the framework of the old Roman Republic. Though emperors held supreme power, they often preserved republican forms, respected senatorial privilege, and avoided overt displays of monarchy.

Diocletian, in contrast, openly embraced the reality of absolute power. In the Dominate, he adopted the title dominus et deus (“lord and god”), a deliberate expression of divine monarchy.

This was a dramatic cultural shift that emphasized the emperor’s sacred authority and placed him above all other institutions. Court ceremony became rigid and formal, with elaborate rituals and strict separation between the emperor and ordinary citizens, including prostration before the imperial person. The Senate’s political relevance was further diminished, and actual power rested in the emperor’s court and military bureaucracy.

Diocletian’s most surprising decisions came at the end of his reign.

In an unprecedented move, Diocletian voluntarily abdicated the throne on May 1, 305, along with Maximian, and retired to his palace in Salona, in the modern-day city of Splitk, Croatia. There, he lived out his final years tending to his gardens, growing cabbages, and resisting efforts to return to power during subsequent political turmoil. He died in 311, likely by suicide, after learning of the collapse of his tetrarchic system and the return of civil war.

Today, you can visit the palace of Diocletian in Split, Croatia. I had the pleasure of visiting it, and it is a very interesting place. It was built as a luxury villa for his retirement. After his death, people moved into his palace, and the city of Split literally grew out of it. Today, it is a UNESCO World Heritage Site and worth visiting if you are on the Dalmatian Coast.

Diocletian’s reign fundamentally reshaped the Roman Empire. His reforms arrested the empire’s decline, reestablished central authority, and influenced the eventual division between Eastern and Western Rome. The Tetrarchy failed as a political system, but its concepts endured, especially in the East, where the Byzantine Empire would inherit Diocletian’s bureaucratic and autocratic legacy.

Likewise, many of his economic reforms failed and may have laid the economic foundations of serfdom centuries later.

Most remarkably, despite being the most powerful person on Earth, he walked away from it all to retire and grow cabbages.