Diocletian

• 1. Introduction

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  Diocletian retired from the most powerful office in the world and went home to grow cabbages. When rivals begged him to return to the throne in 308, he wrote back: "If you could see the cabbages I have planted here with my own hands, you surely would never have thought to request this." It is one of the most disarming lines in the history of Rome, spoken by a man who had governed an empire stretching from Britain to the Euphrates. How a boy born to a family of low status in the Roman province of Dalmatia rose to become the first emperor to voluntarily abdicate his title, and how his twenty-year reign reshaped the structure of Roman rule, is a story that moves through battlefield coups, religious persecution, bureaucratic revolution, and deliberate retirement to a palace by the sea.

• 2. From Dalmatia to Purple

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  Gaius Valerius Diocles was born in Dalmatia, probably near the town of Salona, sometime between 242 and 245. His official birthday was recorded as the 22nd of December. His parents held no social standing; the historian Eutropius preserves the uncertainty of his origins by noting that most writers called him the son of a scribe, while others said he was the son of a freedman belonging to a senator named Anullinus. The first forty years of his life are largely obscure, but he served under the emperors Aurelian and Probus, rising through the military as an Illyricianus. The 12th-century Byzantine chronicler Joannes Zonaras describes him as Dux Moesiae, a commander of forces on the lower Danube. By 282, his position was no longer obscure: Emperor Carus appointed him commander of the Protectores domestici, the elite cavalry unit attached directly to the imperial household, an honor that earned him a consulship in 283.

  Carus died in mysterious circumstances during a Persian campaign, leaving his sons Numerian and Carinus as joint rulers. Numerian traveled in a closed coach on the long journey west from Persia, with court officials explaining that he suffered from an inflammation of the eyes. When the army reached Bithynia, soldiers noticed an odor from the coach. They opened its curtains and found Numerian dead. In Nicomedia that November, the generals and tribunes convened a council to choose a successor. They picked Diocles despite the efforts of the prefect Aper, Numerian's father-in-law, to claim power for himself.

  On the 20th of November 284, the army of the east gathered on a hill five kilometers outside Nicomedia. Diocles was acclaimed their new Augustus. He raised his sword to the sun and swore an oath denying responsibility for Numerian's death. He then named Aper as the killer and executed him in full view of the troops. Within days, Diocles adopted the more Latinate form of his name: Gaius Valerius Diocletianus. The son of a scribe, or a freedman's child, was now Roman emperor.

• 3. The Architecture of Four

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  Ruling alone was dangerous. The assassinations of Aurelian and Probus had demonstrated that a single emperor made a single target. Conflicts burned in every province simultaneously, from Gaul to Syria, Egypt to the lower Danube. Diocletian's solution was to share power, and he did so by degrees. In 286 he raised his fellow officer Maximian first to the rank of Caesar, then elevated him to co-emperor and Augustus. Maximian would govern the west; Diocletian would rule the east as the senior Augustus. To reinforce the bond between two men who had no family connection, they exchanged family names, each adding the other's nomen to his own, creating an artificial kinship through the combined name "Aurelius Valerius". Around 287, Diocletian also took on a divine association, assuming the title Iovius, aligning himself with Jupiter. Maximian took the title Herculius, aligning himself with Hercules. They were not claiming to be gods in the old imperial cult tradition, but rather presenting themselves as the gods' representatives on earth. The shift was deliberate: if emperors derived legitimacy from divine appointment rather than military acclamation, their rivals had less ground to stand on.

  On the 1st of March 293, at Milan, the system expanded again. Maximian gave Flavius Constantius the office of Caesar. On the same day, in either Philippopolis or Sirmium, Diocletian did the same for Galerius Maximianus, who was married to Diocletian's daughter Valeria. Constantius was assigned Gaul and Britain. Galerius received Syria, Palestine, Egypt, and the eastern borderlands. These four men, bound by blood, marriage, adoption, and divine title, formed what is now called the Tetrarchy, from a Greek term meaning "rulership by four". They each governed their own quarter of the empire with their own courts, armies, and administrators. The sons of Maximian and Constantius, Maxentius and Constantine, were brought to Diocletian's court in Nicomedia to prepare for their eventual roles as successors.

• 4. War, Borders, and Bureaucracy

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  Diocletian fought constantly during his reign. He campaigned against the Sarmatians and the Carpi in multiple operations between 285 and 299, defeated the Alamanni in 288, and suppressed uprisings in Egypt between 297 and 298. The Egyptian revolt was triggered by his efforts to bring local taxation into alignment with imperial standards; the usurper Domitius Domitianus declared himself Augustus in July or August of 297, and Alexandria only fell, probably in March 298, after a siege. Diocletian responded to Egypt's rebellion by stripping Alexandria of the right to mint coins independently. Later in 298, the column now known as Pompey's Pillar was erected there in his honor. He then traveled south along the Nile, visiting Oxyrhynchus and Elephantine, and negotiated a peace with the Nobatae and Blemmyes tribes in Nubia, moving Rome's borders north to Philae in exchange for an annual gold stipend.

  The most consequential military episode of the reign involved Persia. In 294, Narseh, a son of Shapur who had been passed over for the Sassanid succession, came to power. He invaded western Armenia and then struck Roman Mesopotamia in 297, inflicting a severe defeat on Galerius near Carrhae and Callinicum. Diocletian publicly humiliated Galerius for the loss, forcing him to walk a mile at the head of the imperial caravan still wearing his purple robes. Galerius was then reinforced from the Danubian provinces and launched a new offensive through Armenia, where the rugged terrain favored Roman infantry over Sassanid cavalry. In two battles, Galerius crushed Narseh. Roman forces captured Narseh's camp, his treasury, his harem, and his wife. Galerius continued down the Tigris and sacked the Persian capital Ctesiphon. The resulting Peace of Nisibis in 299 delivered substantial rewards: Armenia returned to Roman control, Nisibis became the sole conduit for trade between the two empires, and Rome gained five satrapies between the Tigris and Armenia.

  To manage what he had won and held, Diocletian reorganized Roman administration on a sweeping scale. He nearly doubled the number of provinces, from roughly fifty to almost one hundred, grouping them into twelve dioceses, each governed by a vicarius. The historian Warren Treadgold estimates that under Diocletian the number of men in the civil service doubled from 15,000 to 30,000. The army expanded from approximately 390,000 men in 285 to about 580,000. The navy grew from roughly 45,000 to roughly 65,000. To pay for all of it, Diocletian introduced a new tax system built around assessments of heads and land, tied to a regular empire-wide census. Italy, which had long been exempt from taxation, was brought into the system from 290 or 291. From at least 297 on, imperial taxation was standardized and levied at generally higher rates across the empire.

• 5. The Persecution

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  In 299, Diocletian and Galerius took part in a ceremony of sacrifice and divination. The haruspices could not read the entrails of the sacrificial animals and blamed Christians in the imperial household. This small incident triggered the sequence that would produce the Diocletianic Persecution, described by historians as the last, largest, and bloodiest official persecution of Christianity in the Roman Empire, running from 303 to 312.

  Diocletian had already moved against other targets. In a rescript of the 31st of March 302 from Alexandria, he ordered that low-status followers of Mani be executed by the blade, while high-status Manicheans would be sent to work in the quarries of Proconnesus or the mines of Phaeno in southern Palestine. The reasoning he applied to Manichaeanism would soon be applied to Christianity: novelty was a problem, foreign origins were a problem, and any challenge to long-standing Roman religious tradition was a problem.

  Diocletian and Galerius disagreed on how far to go. According to Lactantius, Diocletian believed barring Christians from the bureaucracy and military would be sufficient; Galerius pushed for extermination. They sought advice from the oracle of Apollo at Didyma. The oracle responded that the impious on earth obstructed Apollo's foresight. Court officials identified those impious as Christians. On the 23rd of February 303, Diocletian ordered the newly built church at Nicomedia destroyed, its scriptures burned, and its stores seized. The following day, his first edict against the Christians was published, ordering the destruction of Christian places of worship and scriptures across the empire and prohibiting assembly for worship. A fire in the imperial palace was blamed on Christian conspirators. The palace eunuchs Dorotheus and Gorgonius were executed. A man named Peter Cubicularius was scourged, had salt and vinegar poured into his wounds, and was slowly boiled alive. On the 24th of April 303, the bishop Anthimus was among six individuals decapitated.

  The persecution ultimately failed. Most Christians escaped punishment. Pagan populations were generally unsympathetic to the campaign. Constantius and Maximian did not apply the later edicts in the west, leaving western Christians largely unharmed. The sufferings of martyrs hardened Christian resolve rather than breaking it. Galerius rescinded his own edict in 311, acknowledging that the persecution had not returned Christians to traditional religion. Within twenty-five years of the first edict, the Christian emperor Constantine would rule the empire alone and return all confiscated property to Christians.

• 6. The First Abdication

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  On the 20th of November 303, Diocletian entered Rome and celebrated three milestones simultaneously: the twentieth anniversary of his reign, the tenth anniversary of the Tetrarchy, and a triumph for the Persian war. It would be the last triumph ever held in Rome. He grew quickly impatient with the city. The Romans treated him, in the words Edward Gibbon borrowed from Lactantius, with "licentious familiarity", expecting an aristocratic ruler rather than a monarchic one. On the 20th of December 303, he cut short his stay. He did not even perform the ceremonies marking his ninth consulate in Rome; he conducted them in Ravenna on the 1st of January 304 instead.

  Diocletian's health collapsed during a campaign against the Carpi. He traveled in a litter. By the late summer of 304 he had reached Nicomedia, and on the 20th of November he appeared in public to dedicate the opening of a circus beside his palace. He collapsed shortly after. Through the winter of 304 to 305, he remained inside the palace entirely. Rumors spread that he had already died and that the news was being suppressed until Galerius could consolidate power. On the 13th of December it was falsely announced that Diocletian had taken his own life, and the city mourned before public declarations confirmed he was still alive. When he reappeared on the 1st of March 305, witnesses found him emaciated and barely recognizable.

  On the 1st of May 305, Diocletian called an assembly at the same hill outside Nicomedia where, twenty years earlier, he had been acclaimed emperor. Before a statue of Jupiter, he told the gathered soldiers and officials that he was weak, that he needed rest, that he was passing the duty of empire to someone stronger. In tears, he removed the purple vestments. He had expected the crowd to acclaim Constantine and Maxentius as the new Caesars; instead, strangers named Severus II and Maximinus II received the titles. Constantine and Maxentius were passed over entirely. It was a wound in the Tetrarchic system that would eventually prove fatal.

• 7. The Palace and the Cabbages

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  Diocletian retired to a heavily fortified compound by the small town of Spalatum on the Dalmatian coast, near the provincial administrative center of Salona where he was probably born. The palace he built there was designed as a permanent home. UNESCO designated it a World Heritage Site in 1979, and it forms the historic core of the modern city of Split in Croatia.

  His co-emperor Maximian retired to villas in Campania or Lucania, far from politics but close enough that the two remained in regular contact. In 308, at a conference at Carnuntum in what is now Petronell-Carnuntum, Austria, Galerius convened a meeting at which Diocletian and Maximian were both present on the 11th of November to see Galerius appoint Licinius as Augustus in place of Severus, who had been killed by Maxentius. Delegates begged Diocletian to return to the throne. He declined with the line about his cabbages.

  The tetrarchic system he had designed did not survive him. Constantine's rise and Maxentius's usurpation tore it apart. Maximian made a third attempt to reclaim power, was forced to take his own life, and was subjected to damnatio memoriae, the formal erasure of his memory. In Diocletian's own palace, statues and portraits of Maximian were pulled down and destroyed. Diocletian's wife Prisca and their daughter Valeria had their property confiscated and were exiled to Syria in 311 after Valeria refused the emperor Maximinus Daza's proposal of marriage. In 315, Licinius had both of them executed.

  Diocletian died on the 3rd of December 311, or possibly 312. Some speculated he ended his own life in despair, but Gibbon wrote that this was "very doubtful". He had outlived most of the system he built, watched a man he loved have his memory erased, and saw the last persecution of Christians fail to suppress a faith that would, within a generation, become the empire's favored religion. The palace at Spalatum, tended by the man who once commanded half the world, would still be standing seventeen centuries later.