Diocletian – Rome’s First Retired Emperor

Today’s video is brought to you by Athletic Greens. More on them in just a bit.

The first century AD was not a good time for the Roman Empire. The eagle standard had lost much of its luster, and Rome was no longer the invincible juggernaut that could make the rest of Europe tremble at the might of its legions. The death of Emperor Severus Alexander in 235 AD marked the end of the Severan Dynasty and plunged the empire into complete anarchy, known as the Crisis of the Third Century. With no heir, numerous generals and politicians tried to claim the throne for themselves, but none had the strength to stand undisputed above the rest.

This political instability was accompanied by constant incursions from barbarian tribes, civil wars, peasant rebellions, the debasement of currency, a collapsing economy, and even a plague for good measure. The Roman Empire saw over 20 emperors in a 50-year period, not counting the dozens of pretenders to the throne who never got to enjoy their time in the spotlight. Most of them only lasted briefly and accomplished very little. It wasn’t until an emperor named Aurelian came along in 270 AD that he managed to restore some semblance of stability, but he was killed after only a few years, leaving his work unfinished.

On the brink of chaos, the very existence of the empire was under threat. If another capable emperor didn’t finish what Aurelian had started, then along came Diocletian. He had some unconventional ideas about how to rule the Roman Empire, and they were just crazy enough to work. So, did they? Let’s find out as we examine the life and career of Diocletian.

Diocletian was born on December 22nd, circa 245 AD, in the Roman province of Dalmatia, likely in the ancient city of Salona, located in modern-day Croatia. He came from humble origins and was known as Diocles at birth, although he later adopted the more grandiose title of Gaius Aurelius Valerius Diocletianus. Due to his low status, not much was recorded about him, so the first half of Diocletian’s life has been lost to history. His father was either a scribe or a former slave who once belonged to a senator named Anulinus. Neither his father’s nor his mother’s names have been recorded. All we know is that at some point, Diocletian married a woman named Prisca, and together they had a daughter named Valeria.

As we’ve mentioned in several other biographical videos, your average Roman had two basic ways to climb the social ladder: through politics or the military. Politics had a rigid career path called the cursus honorum, which included a series of public offices necessary to become a senator. This route was out of reach for most Romans since it required a lot of money or connections, or ideally both. The military approach was always more straightforward: enlist, serve, and get promoted. Diocletian chose the latter.

We don’t know where he went or what he did, but we presume he performed well as a soldier. Around 282 AD, he was promoted to domesticus regis, the leader of the Imperial Cavalry that protected the emperor, indicating he was a skilled warrior and military commander.

The emperor at that time was a man named Carus, who reigned for less than a year. When Carus adopted the imperial title of Augustus, he bestowed the title of Caesar to his two sons, Numerian and Carinus, making them junior emperors and heirs to the throne. In early 283 AD, Carus decided to renew the rivalry with one of Rome’s classic foes, Persia, now in the form of the Sasanian Empire. He made his way into East Mesopotamia and fought King Bahram II, achieving victory and even capturing the Sasanian capital of Ctesiphon. However, he didn’t know when to walk away from the table. Instead of returning to Rome a triumphant hero, he pressed on, driven by the long-standing ambition of many Roman emperors to conquer all of Persia. Carus didn’t achieve his goal; instead, he died sometime during the summer of 283.

We don’t know the exact circumstances of his death, but some ancient sources claim he was struck by lightning, while a sudden illness seems more plausible. After Carus’s death, the mantle of Augustus was passed on to his sons. Carinus was in Gaul at the time trying to suppress revolts, but Numerian, who had been alongside his father fighting the Sasanian forces, assumed control of the army and tried to settle things before marching back to Rome. However, he fell ill, and by the time they reached Nicomedia in November 284 AD, the soldiers discovered that they had been carrying around a corpse, as Numerian had been dead for some time.

An emergency council was held after Numerian’s death, with all of his top generals and advisors in attendance. The choice for succession was mainly between two candidates: Diocletian and the commander of the Imperial Guard, Aper. As a lifelong military man, Diocletian had the support of the army, and he made everyone’s choice easier when he accused Aper of assassinating Numerian and then killed him in front of the entire army. Diocletian then swore an oath that he had nothing to do with Numerian’s death and was proclaimed the new Roman Emperor.

However, Diocletian still had to deal with Carinus. If Diocletian had one trait that helped him succeed where many previous emperors failed, it was his awareness and acceptance of his limitations. Unlike the stereotypical Roman emperor who went mad with power, Diocletian knew he couldn’t do everything himself and never even tried. His entire reign was based on distributing power to others so they could share the load.

Diocletian selected a man named Lucius Domitius Aurelianus as his co-emperor. This decision firmly rejected Carinus’s authority and any idea that they would rule together, especially with Diocletian as the junior colleague. Diocletian knew the golden rule of a long and stable reign: of Rome’s three major groups—the Senate, the army, and the people—you needed the support of at least two of them to avoid being poisoned during dinner or revolted against.

Diocletian already had the army on his side, which is why he didn’t appoint a general as his co-consul but instead chose a lifelong politician. With battle lines drawn, the two would-be emperors gathered their men and met at the Battle of Margus River in July 285 AD. Carinus was the odds-on favorite due to a larger army, but he was killed by one of his own men at the outset of the battle, allowing Diocletian to claim victory.

With Carinus dead, the path was clear for Diocletian to become the sole ruler of the Roman Empire. However, he understood that the empire was too large for one person to rule alone. He willingly relinquished some of his power and divided the Roman Empire into two halves, with one emperor ruling the West and another ruling the East.

Diocletian selected Maximian as his co-emperor, who also came from humble origins. He put Maximian on a trial run first, giving him the title of Caesar before promoting him to Augustus in 286 AD. Diocletian had never been a fan of Rome, considering it a city full of spoiled individuals. Therefore, he chose to reign over the eastern half of the empire and made Nicomedia its new capital, marking a significant shift in the center of power.

With administrative issues settled, the two emperors moved to resolve various armed conflicts. Maximian faced challenges from Germanic tribes, while Diocletian dealt with the Sasanian Empire. In 293 AD, Diocletian instituted the Tetrarchy, or rule of four, where each Augustus would select a junior emperor or Caesar who would eventually become Augustus themselves.

Diocletian selected Constantius Chlorus as Maximian’s Caesar and Galerius as his own. The Caesars were experienced military commanders expected to handle the bulk of the fighting. Constantius faced the hardest task, dealing with the usurper Carausius, who had claimed Britain for himself. Fortunately for Constantius, Carausius was betrayed and assassinated.

In 297 AD, Diocletian had to deal with a usurper in Egypt named Achillius, which he handled straightforwardly. However, the Sasanian Empire declared war on Rome, leading to a pitched battle that resulted in a decisive Roman victory.

As the new century dawned, Diocletian turned his gaze inward to address threats from within, particularly the rise of Christianity. Diocletian was not a fan of Christianity and believed it caused instability. Thus, he initiated some of the harshest persecutions against Christians, known as the Great Persecution, which lasted from 303 to 311 AD.

In 304 AD, Diocletian suffered a significant health scare, prompting him to consider retirement. On May 1, 305 AD, he abdicated, allowing Galerius to become the new Augustus. Diocletian retreated to his homeland of Dalmatia, where he spent his time in his gardens. He died peacefully of old age circa 311 AD, having witnessed the collapse of the Tetrarchy into chaos.

Although the idea of the Tetrarchy might have seemed good on paper, it relied on four men being satisfied with only a fraction of the power. Once the original four were gone, it quickly devolved into betrayals, rebellions, and conspiracies, reminiscent of the chaotic Rome of old.