Diocletian

Anyone asking who was Diocletian must begin far from Rome, on the eastern shore of the Adriatic. He was born Diocles on December 22, 244 CE, in or near Doclea in the Roman province of Dalmatia, in what is now the Balkans ^[1]. His family was humble, and ancient writers offer conflicting claims about his parents: some said his father was a scribe, others that the family had once been enslaved and later freed by a senator named Anullinus ^[2]. Nothing in his background suggested a future ruler, and no reliable record survives of his education or childhood.

What Dalmatia did offer a poor young man of ability was the army. During the middle decades of the third century the Roman Empire was in constant emergency. Emperors were murdered or fell in battle at a brutal pace, frontiers on the Rhine, Danube, and Euphrates gave way, plague and inflation gnawed at cities, and the Illyrian provinces became the empire's chief recruiting ground ^[3]. Diocles enlisted and served under a succession of soldier emperors, and like other tough Danubian officers of his generation he advanced on merit rather than birth ^[1].

By the early 280s he had reached high rank. Under the emperor Carus he commanded the protectores domestici, the elite cavalry guard attached to the imperial household, and he accompanied the emperor's son Numerian on campaign in the East ^[2]. That posting placed him at the center of events when the reigning dynasty suddenly disintegrated.

Carus died in 283 during a Persian campaign, reportedly struck by lightning, and his son Numerian died in mysterious circumstances the following year while the army marched home through Asia Minor ^[2]. When the young emperor's death was discovered near Nicomedia in November 284, the troops looked for both a culprit and a successor. They found the first in Aper, the praetorian prefect and Numerian's father in law, and the second in Diocles. Ancient accounts describe the new emperor killing Aper with his own sword in front of the assembled soldiers, publicly blaming him for the death ^[3].

Proclaimed emperor on November 20, 284, he Latinized his Greek name to Gaius Aurelius Valerius Diocletianus ^[1]. His position was far from secure. Carus's surviving son Carinus still ruled the West with a veteran army, and the two rivals met in battle at the Margus River in the Balkans in 285. Carinus apparently had the upper hand until he was killed by one of his own officers, leaving Diocletian sole master of the Roman world ^[2].

His first major decision revealed the political instinct that would define his reign. Rather than attempt to govern a besieged empire alone, in 285 he appointed his fellow soldier Maximian as Caesar, a junior emperor, and promoted him to full Augustus in 286 ^[1]. Maximian took charge of the West while Diocletian ruled the East from Nicomedia. It was an unsentimental recognition that the empire's problems, from Gallic rebellions to Persian pressure, could no longer be handled by a single man in a single place ^[3].

The list of Diocletian achievements is longer than that of almost any emperor since Augustus. His most famous creation came in 293, when he expanded the two man college into the Tetrarchy, or rule of four. Two senior emperors, the Augusti Diocletian and Maximian, were each paired with a junior Caesar: Galerius in the East and Constantius in the West ^[1]. Each of the four watched a stretch of frontier from his own regional capital, and the arrangement was cemented by marriages and adoptions rather than by blood succession. For two decades the system worked. Usurpations, which had destroyed emperor after emperor for fifty years, almost ceased, because any rebel now faced four rulers instead of one ^[4].

Military results followed. Between them the tetrarchs suppressed the Bagaudae uprisings in Gaul, recovered Britain from the breakaway regimes of Carausius and Allectus, defeated Sarmatian and Carpi incursions on the Danube, and crushed a serious revolt in Egypt, where Diocletian personally besieged Alexandria in 297 to 298 ^[2]. The greatest triumph came against Persia. After an initial defeat, the Caesar Galerius routed King Narses in Armenia in 298, capturing the royal household. The resulting peace of Nisibis gave Rome territory beyond the Tigris and a favorable eastern frontier that lasted about forty years ^[3].

Behind the frontiers Diocletian rebuilt the machinery of the state. He roughly doubled the number of provinces to more than one hundred, grouping them into twelve larger units called dioceses, each supervised by a deputy called a vicarius, and he separated civil administration from military command so that no governor controlled both taxes and troops ^[1]. A new census based taxation system, assessed on units of land and labor called iuga and capita, made the burden more predictable and funded an enlarged army ^[4]. He also transformed the emperor's image, adopting the title Iovius (belonging to Jupiter), the diadem and jeweled robes of an eastern monarch, and court rituals in which officials prostrated themselves before him. Historians use the word dominate for this new, openly autocratic style of rule ^[3].

Not every measure succeeded. His Edict on Maximum Prices of 301, which fixed legal ceilings on the cost of goods, wages, and freight across the empire, aimed to strangle inflation, but goods simply vanished from the markets and the law became a dead letter ^[5]. Even so, the surviving inscribed copies of the edict remain one of the most valuable economic documents to come down from antiquity, listing prices for everything from lentils to lions ^[5].

The darkest chapter of the reign opened on February 23, 303, when soldiers demolished the Christian church that stood within sight of the palace at Nicomedia. The next day Diocletian issued the first of four edicts against the Christians, ordering scriptures burned, churches razed, and believers stripped of legal rights; later edicts required clergy and then all inhabitants to sacrifice to the gods on pain of imprisonment or death ^[6].

Why an emperor who had tolerated Christians for nearly twenty years turned on them remains debated. The Christian writer Lactantius, who taught rhetoric at Nicomedia and knew the court, blamed the Caesar Galerius for pushing a reluctant Diocletian toward violence, though Lactantius wrote as a hostile witness ^[6]. Modern historians also point to Diocletian's deep religious conservatism: a ruler who had staked his legitimacy on Jupiter's protection saw the refusal of sacrifice as a threat to the divine contract securing the empire ^[4].

The Great Persecution was applied unevenly. In Gaul and Britain, Constantius did little beyond pulling down some buildings, while in the East, under Galerius and later Maximinus Daia, executions continued for years ^[3]. The policy failed utterly. Christian communities endured, martyrdom stories multiplied, and in 311 the dying Galerius issued an edict of toleration admitting that coercion had not worked. Within a generation Constantine, son of Constantius, would make Christianity the favored religion of the empire, an outcome that has colored Diocletian's reputation ever since ^[6].

On May 1, 305, in a ceremony outside Nicomedia, Diocletian did something no Roman emperor had ever done: he abdicated voluntarily, compelling the reluctant Maximian to step down in the West on the same day ^[1]. The Caesars Galerius and Constantius became the new Augusti, and two new Caesars were appointed. Illness lay behind the decision in part, since Diocletian had nearly died during the winter of 304 to 305, but the abdication also expressed his conviction that orderly, planned succession should replace murder and civil war ^[2].

He withdrew to a fortified seaside palace he had built near Salona on the Dalmatian coast, at the place now called Split in Croatia. The complex, covering several acres, combined a military camp's walls with a luxurious villa, a temple of Jupiter, and the emperor's own mausoleum ^[7]. There he lived as a private citizen, and a famous story preserved in later sources has him refusing an appeal to retake power in 308 with the reply that if his petitioners could see the cabbages he had planted with his own hands, they would not ask him to trade his garden for the storms of ambition ^[2].

The retirement was not entirely peaceful. The Tetrarchy fractured within a year of his departure, as Constantine and Maxentius seized power outside the approved order and the empire slid back toward civil war. Diocletian watched his life's political design come apart, and his final years brought personal grief: his wife Prisca and daughter Valeria fell into the power of hostile emperors and were later executed ^[3]. He died at his palace on December 3, 316 CE, and was laid to rest in the mausoleum he had prepared there ^[7].

Any honest Diocletian biography must weigh destruction against reconstruction. To Christian tradition he was the last great persecutor, remembered in martyrologies across Europe and the Middle East, and the era of the martyrs was long dated from the start of his reign in 284 ^[6]. To historians of government he is the second founder of the Roman state. His provincial reorganization, separation of civil and military power, tax census, enlarged bureaucracy, and elevated court ceremonial defined the later Roman and Byzantine empires for centuries ^[4].

The Tetrarchy itself did not survive him, yet its underlying idea, that the empire was too large for one ruler and could be divided administratively between East and West, proved durable. The division Diocletian improvised for practical reasons foreshadowed the permanent split of 395 and, ultimately, the separate destinies of Rome and Constantinople ^[3]. His price edict, his rescripts on law, and the porphyry statue group of the four embracing tetrarchs now set into a corner of St Mark's in Venice give his age an unusually rich material record ^[5].

The most tangible monument is the palace at Split. After the fall of the western empire, refugees from nearby Salona moved inside its walls, and a living city grew within the emperor's retirement home. His mausoleum was converted into the cathedral of Split, so that the tomb of Christianity's fiercest persecutor became, by a twist few could have predicted, a church dedicated to a martyr of his own persecution. The palace was inscribed as a UNESCO World Heritage Site in 1979 and remains among the best preserved Roman monuments anywhere ^[7]. Among the many Diocletian facts that surprise modern readers, that afterlife of his home may be the most fitting: a builder of systems whose stones outlasted every system he built.