Gaius Aurelius Valerius Diocletianus (ca. December 22 244 – December 3 311), born Diocles (Greek: Διοκλής) and commonly known as Diocletian was Roman Emperor from November 20 284 to May 1 305. Born to a Dalmatian family of low status, he rose through the ranks of the military to become cavalry commander to the emperor Carus. After the deaths of Carus and his son Numerian on campaign in Persia, Diocletian was acclaimed emperor by the army. A brief confrontation with Carus' other surviving son Carinus at the Battle of the Margus removed the only other claimant to the title. With his ascension to power, he ended the Crisis of the Third Century, marking the difference between the classical world and the world of late antiquity. Diocletian appointed fellow-officer Maximian his Augustus, his senior co-emperor, in 285. He delegated further on March 1 293, appointing Galerius and Constantius as Caesars, junior co-emperors. Under this "Tetrarchy", or "rule of four", each emperor would rule over a quarter-division of the empire. In campaigns against Sarmatian and Danubian tribes (285–90), the Alamanni (288), and usurpers in Egypt (297–98), Diocletian secured the empire's borders and purged it of threats to his power. In 299, Diocletian led negotiations with Sassanid Persia, the empire's traditional enemy, and achieved a lasting and favorable peace.
Diocletian separated and enlarged the empire's civil and military services and re-organized the empire's provincial divisions, establishing the largest and most bureaucratic government in the history of the empire. He established new administrative centers in Nicomedia, Mediolanum, Antioch, and Trier, closer to the empire's frontiers than the traditional capital at Rome had been. Building on third-century trends towards absolutism, Diocletian styled himself an autocrat, elevating himself above the empire's masses with imposing forms of court ceremonial and architecture. Bureaucratic and military growth, constant campaigning, and construction projects increased the state's expenditures, and necessitated a comprehensive tax reform. From at least 297 on, imperial taxation was standardized, made more equitable, and levied at generally higher rates.
Not all Diocletian's plans were successful; the Edict on Maximum Prices (301), Diocletian's attempt to curb inflation via price controls, was unsuccessful, counterproductive, and quickly ignored. Although effective while he ruled, Diocletian's Tetrarchic system collapsed after his abdication under the competing dynastic claims of Maxentius and Constantine, sons of Maximian and Constantius respectively. The Diocletianic Persecution (303–11), the empire's last, largest, and bloodiest official persecution of Christianity, did not destroy the empire's Christian community; indeed, after 324 Christianity became the empire's preferred religion under its first Christian emperor, Constantine. In spite of his failures, Diocletian's reforms fundamentally changed the structure of Roman imperial government and helped stabilize the empire economically and militarily, enabling an empire that had seemed near the brink of collapse in Diocletian's youth to remain essentially intact for another hundred years. Weakened by illness, Diocletian left the imperial office on May 1 305, and became the first Roman emperor to voluntarily abdicate the position. He lived out his retirement in his palace on the Dalmatian coast, tending to his vegetable gardens.
Carus, already sixty, wished to establish a dynasty; he immediately elevated his sons Carinus and Numerian to the rank of Caesar. In 283, Carus raised Carinus to the title Augustus, left him in charge of the care of the West, and moved with Numerian, Diocles, and the praetorian prefect Aper to the East, against the Sassanid Empire. The Sassanids had been embroiled in a succession dispute since the death of Shapur, and were in no position to oppose Carus' advance. According to Zonaras, Eutropius, and Festus, Carus won a major victory against the Persians, taking Seleucia and the Sassanid capital of Ctesiphon (near modern Al-Mada'in, Iraq), cities on opposite banks of the Tigris. In celebration, Carus and his sons took the title Persici maximi. Carus died in July or early August, reportedly struck by lightning.
Carus' death left his unpopular sons Numerian and Carinus as the new Augusti. Carinus quickly made his way to Rome from Gaul, and arrived by January 284; Numerian lingered in the East. The Roman retreat from Persia was orderly and unopposed, for the Persian King, Bahram II, was still struggling to establish his authority. By March 284 Numerian had only reached Emesa (Homs) in Syria; by November, only Asia Minor. In Emesa he was apparently still alive and in good health, as he issued the only extant rescript in his name there. After Emesa, Numerian's staff, including the prefect Aper, reported that Numerian suffered from an inflammation of the eyes, and had to travel in a closed coach. When the army reached Bithynia, some of Numerian's soldiers smelled an odor reminiscent of a decaying corpse emanating from the coach. They opened its curtains. Inside, they found Numerian, dead.
Aper officially broke the news in Nicomedia (İzmit) in November. Numerianus' generals and tribunes called a council for the succession, and chose Diocles as emperor, in spite of Aper's attempts to garner support. On November 20 284, the army of the east gathered on a hill three miles outside Nicomedia. The army unanimously saluted their new Augustus, and Diocles accepted the purple imperial vestments. He raised his sword to the light of the sun, and swore an oath disclaiming responsibility for Numerian's death. He asserted that Aper had killed Numerian and concealed it. In full view of the army, Diocles drew his blade and killed Aper. Soon after Aper's death, Diocles changed his name to the more Latinate "Diocletianus",, in full Gaius Aurelius Valerius Diocletianus.
After his accession, Diocletian and Lucius Caesonius Bassus were named as consuls. They assumed the fasces in place of Carinus and Numerianus. Bassus was a member of a Campanian senatorial family, a former consul and a proconsul of Africa. He had been chosen by Probus for signal distinction. He was a man skilled in areas of government where Diocletian, presumably, had no experience. Diocletian's elevation of Bassus as consul symbolized his rejection of Carinus' government in Rome, his refusal to accept second-tier status to any other emperor, and his willingness to continue the long-standing collaboration between the empire's senatorial and military aristocracies. It also tied his success to that of the Senate, whose support he would need in an advance on Rome.
Diocletian was not the only challenger to Carinus' rule; the usurper M. Aurelius Julianus, Carinus' corrector Venetiae, controlled northern Italy and Pannonia. Julianus took power following Diocletian's accession. He minted coins from the mint at Siscia (Sisak, Croatia) declaring himself as emperor and promising freedom. It was all good press for Diocletian, and aided in his portrayal of Carinus as a cruel and oppressive tyrant. Julianus' forces were weak, however, and were handily dispersed when Carinus' armies moved from Britain to northern Italy. With the East under control, Diocletian was clearly a greater threat. Over the winter of 284–5, Diocletian advanced west across the Balkans. In the spring, some time before the end of May, his armies met Carinus' across the river Margus (Great Morava) in Moesia. In modern accounts, the site has been located between the Mons Aureus (Seone, west of Smederevo) and Viminacium, near modern Belgrade, Serbia.
Despite having the stronger army, Carinus held the weaker position. His rule was unpopular; it was subsequently alleged that Carinus had mistreated the Senate and seduced the wives of his officers. It is possible that Flavius Constantius, the governor of Dalmatia and Diocletian's associate in the household guard, had already defected to Diocletian in the early spring. When the Battle of the Margus began, Carinus' prefect Aristobulus also defected. In the course of the battle, Carinus was killed by his own men. Following Diocletian's victory, both the western and the eastern armies acclaimed him emperor. Diocletian exacted an oath of allegiance from the defeated army and departed for Italy.
Diocletian replaced the prefect of Rome with his consular colleague Bassus. Most officials who had served under Carinus, however, retained their offices under Diocletian. In an act the epitomator Aurelius Victor denotes as unusual act of clementia, Diocletian did not kill or depose Carinus' traitorous praetorian prefect and consul Ti. Claudius Aurelius Aristobulus, but confirmed him in both roles, and later gave him the proconsulate of Africa and the rank of urban prefect. The other figures who retained their offices might have also betrayed Carinus.
Recent history had demonstrated that sole rulership was dangerous to the stability of the empire. The assassinations of Aurelian (r. 270–275) and Probus testified to that truth. Conflict boiled in every province of the empire, from Gaul to Syria, from Egypt to the lower Danube. It was too much for a single person to control, and Diocletian needed a lieutenant. At some time in 285 at Mediolanum (Milan, Italy), Diocletian raised his fellow-officer Maximian to the office of Caesar, making him co-emperor.
The concept of dual rulership was nothing new to the Roman Empire. Augustus, the first emperor (r. 27 BC–AD 14), had shared power with his colleagues, and more formal offices of co-emperor had existed from Marcus Aurelius (r. 161–180) on. Most recently, the emperor Carus and his sons had ruled together, albeit unsuccessfully. Diocletian was in a less comfortable position than most of his predecessors, as he had a daughter, Valeria, but no sons. His co-ruler had to be from outside his family. He could not, therefore, be easily trusted. Some historians state that Diocletian, like some emperors before him, adopted Maximian as his filius Augusti, his "Augustan son", upon his appointment to the throne. This argument has not been universally accepted.
The relationship between Diocletian and Maximian was quickly couched in religious terms. Circa 287 Diocletian assumed the title Iovius, and Maximian assumed the title Herculius. The titles were probably meant to convey certain characteristics of their associated leaders; Diocletian, in Jovian style, would take on the dominating roles of planning and commanding; Maximian, in Herculian mode, would act as Jupiter's heroic subordinate. For all their religious connotations, the emperors were not "gods" in the tradition of the Imperial cult—although they may have been hailed as such in Imperial panegyrics. Instead, they were seen as the gods' representatives, effecting their will on earth. The shift to divine sanctification from military acclamation took the power to appoint emperors away from the army. Religious legitimization elevated Diocletian and Maximian above potential rivals in a way military power and dynastic claims could not. After his acclamation, Maximian was dispatched to fight the rebel Bagaudae in Gaul. Diocletian returned to the East.
Around the same time, perhaps in 287, Persia relinquished claims on Armenia and recognized Roman authority over territory to the west and south of the Tigris. The western portion of Armenia was incorporated into the Roman empire and made a province. Tiridates III, Arsacid claimant to the Armenian throne and Roman client, had been disinherited and forced to take refuge in the Roman empire after the Persian conquest of 252/3. In 287, he returned to lay claim to the eastern half of his ancestral domain. He encountered no opposition. Bahram II's gifts were widely recognized as symbolic of a victory in the ongoing conflict with Persia; Diocletian was hailed as the "founder of eternal peace". The events might have represented a formal end to Carus' eastern campaign, which probably ended without an acknowledged peace. At the conclusion of discussions with the Persians, Diocletian re-organized the Mesopotamian frontier and fortified the city of Circesium (Buseire, Syria) the Euphrates.
Maximian realized that he could not immediately suppress the rogue commander, and so, for the whole campaigning season of 287, campaigned against tribes beyond the Rhine instead. The following spring, as Maximian prepared a fleet for an expedition against Carausius, Diocletian returned from the East to meet Maximian. The two emperors agreed on a joint campaign against the Alamanni. Diocletian invaded Germania through Raetia while Maximian progressed from Mainz. Each emperor burned crops and food supplies as he went, destroying the Germans' means of sustenance. The two men added territory to the empire and allowed Maximian to continue preparations against Carausius without further disturbance. On his return to the East, Diocletian managed what was probably another rapid campaign against the resurgent Sarmatians. No details survive, but surviving inscriptions indicate that Diocletian took the title Sarmaticus Maximus after 289.
In the East, Diocletian engaged in diplomacy with desert tribes in the regions between Rome and Persia. He might have been attempting to persuade them to ally themselves with Rome, thus reviving the old, Rome-friendly, Palmyrene sphere of influence, or simply attempting to reduce the frequency of their incursions. No details survive for these events. Some of the princes of these states were Persian client kings; a disturbing fact in light of increasing tensions with that kingdom. In the West, Maximian lost the fleet built in 288 and 289, probably in the early spring of 290. The panegyrist who refers to the loss suggests that its cause was a storm, but this might simply be the panegyrist's attempt to play down the embarrassment of defeat. Diocletian broke off his tour of the Eastern provinces soon thereafter. He returned with haste to the West, reaching Emesa by May 10 290, and Sirmium on the Danube by July 1 290.
Diocletian met Maximian in Milan in the winter of 290–1, either in late December 290 or January 291. The meeting was undertaken with a sense of solemn pageantry. The emperors spent most of their time in public appearances. It has been surmised that the ceremonies were arranged to demonstrate Diocletian's continuing support for his faltering colleague. A deputation from the Roman Senate met with the emperors, renewing that body's infrequent contact with the imperial office. The choice of Milan over Rome further snubbed the capital's pride. The panegyric detailing the events implies that the true center of the empire is not Rome, but where the emperor sits: "...the capital of the Empire appeared to be there, where the two emperors met. Decisions on matters of politics and war were most likely made, but they were made in secret. The Augusti would not meet again until 303.
This arrangement is called the Tetrarchy, from a Greek term meaning "rulership by four". The Tetrarchic emperors were more or less sovereign in their own lands, and they travelled with their own imperial courts, administrators, secretaries, and armies. They were joined by blood and marriage; Diocletian and Maximian now styled themselves as brothers. The senior co-emperors formally adopted Galerius and Constantius as sons in 293. These relationships implied a line of succession. Galerius and Constantius would become Augusti after Diocletian and Maximian's departure. Maximian's son Maxentius, and Constantius' son Constantine would then become Caesars. In preparation for their future roles, Constantine and Maxentius were taken to Diocletian's court in Nicomedia.
Diocletian spent the spring of 293 traveling with Galerius from Sirmium to Byzantium (Istanbul, Turkey). Diocletian then returned to Sirmium, where he would remain for the following winter and spring. He campaigned against the Sarmatians again in 294, probably in the autumn, and won a victory against them. The defeat kept the Sarmatians from the Danube provinces for a long time. He built forts north of the Danube, at Aquincum (Budapest, Hungary), Bononia (Vidin, Bulgaria), Ulcisia Vetera, Castra Florentium, Intercisa (Dunaújváros, Hungary), and Onagrinum (Begeč, Serbia). The new forts became part of a new defensive line called the Ripa Sarmatica. In 295 and 296 Diocletian campaigned in the region again, and won a victory over the Carpi in the summer of 296. By the end of his reign, Diocletian had secured the entire length of the Danube, provided it with forts, bridgeheads, highways, and walled towns, and sent fifteen or more legions to patrol the region. The defense came at a heavy cost, but was a significant achievement in an area difficult to defend.
Galerius, meanwhile, was engaged in disputes in Upper Egypt. He would return to Syria in 295 to fight the revanchist Persian Empire. Diocletian's attempts to bring the Egyptian tax system in line with imperial standards stirred discontent, and a revolt swept the region after Galerius' departure. The usurper L. Domitius Domitianus declared himself Augustus in July or August 297. Much of Egypt, including Alexandria, recognized his rule. Diocletian moved into Egypt to suppress him, first putting down rebels in the Thebaid in the autumn of 297, then moving on to besiege Alexandria. Domitianus died in December 297, by which time Diocletian had secured control of the Egyptian countryside. Alexandria, whose defense was organized under Diocletian's former corrector Aurelius Achilleus, held out until a later date, probably March 298.
Bureaucratic affairs were completed during Diocletian's stay: a census took place, and Alexandria, in punishment for its rebellion, lost the ability to mint independently. Diocletian's reforms in the region, combined with those of Septimus Severus, brought Egyptian administrative practices much closer to Roman standards. Diocletian travelled south along the Nile the following summer, where he visited Oxyrhynchus and Elephantine. In Nubia, he made peace with the Nobatae and Blemmyes tribes. Under the terms of the peace treaty Rome's borders moved north to Philae and the two tribes received an annual gold stipend. Diocletian left Africa quickly after the treaty, moving from Upper Egypt in September 298 to Syria in February 299. He met up with Galerius in Mesopotamia.
Narseh declared war on Rome in 295 or 296. He appears to have first invaded western Armenia, where he seized the lands delivered to Tiridates in the peace of 287. Narseh moved south into Roman Mesopotamia in 297, where he inflicted a severe defeat on Galerius in the region between Carrhae (Harran, Turkey) and Callinicum (Ar-Raqqah, Syria) (and thus, the historian Fergus Millar notes, probably somewhere on the Balikh river). Diocletian may or may not have been present at the battle, but he quickly divested himself of all responsibility. In a public ceremony at Antioch, the official version of events was clear: Galerius was responsible for the defeat; Diocletian was not. Diocletian publicly humiliated Galerius, forcing him to walk for a mile at the head of the imperial caravan, still clad in the purple robes of the emperor.
Galerius was reinforced, probably in the spring of 298, by a new contingent collected from the empire's Danubian holdings. Narseh did not advance from Armenia and Mesopotamia, leaving Galerius to lead the offensive in 298 with an attack on northern Mesopotamia via Armenia. It is unclear if Diocletian was present to assist the campaign; he might have returned to Egypt or Syria. Narseh retreated to Armenia to fight Galerius' force, to Narseh's disadvantage; the rugged Armenian terrain was favorable to Roman infantry, but unfavorable to Sassanid cavalry. In two battles, Galerius won major victories over Narseh. During the second encounter, Roman forces seized Narseh's camp, his treasury, his harem, and his wife. Galerius continued moving down the Tigris, and took the Persian capital at Ctesiphon before returning to Roman territory along the Euphrates.
A stretch of land containing the later strategic strongholds of Amida (Diyarbakır, Turkey) and Bezabde came under firm Roman military occupation. With these territories, Rome would have an advance station north of Ctesiphon, and would be able to slow any future advance of Persian forces through the region. The Tigris was said to have become the boundary between the two empires, but what this means is unclear, as the satrapies listed all lie on the far side of the river. Millar suggests that the satrapies might have been held under a loose Roman hegemony, without military occupation. At the conclusion of the peace, Tiridates regained both his throne and the entirety of his ancestral claim. Rome secured a wide zone of cultural influence, which led to a wide diffusion of Syriac Christianity from a center at Nisibis in later decades, and the eventual Christianization of Armenia.
Antioch was Diocletian's primary residence from 299 to 302. He visited Egypt once, over the winter of 301–2, and issued a grain dole in Alexandria. Following some public disputes with Manicheans, Diocletian ordered that the leading followers of Mani be burnt alive along with their scriptures. In a March 31 302 rescript from Alexandria, he declared that low-status Manicheans must be executed by the blade, and high-status Manicheans must be sent to work in the quarries of Proconnesus (Marmara Island, Turkey) or the mines of Phaeno in southern Palestine. All Manichean property was to be seized and deposited in the imperial treasury. Diocletian found much to be offended by in Manichean religion: its novelty, its alien origins, the way it corrupted the morals of the Roman race, and its inherent opposition to long-standing religious traditions. Manichaeanism was also supported by Persia at the time, compounding religious dissent with international politics. Excepting Persian support, the reasons why he disliked Manichaenism were equally applicable, if not more so, to Christianity, his next target.
On February 23 303, Diocletian ordered that the newly built church at Nicomedia be razed. He demanded that its scriptures be burned, and seized its precious stores for the treasury. The next day, Diocletian's first "Edict against the Christians" was published. The edict ordered the destruction of Christian scriptures and places of worship across the Empire, and prohibited Christians from assembling for worship. Before the end of February, a fire destroyed part of the imperial palace. Galerius convinced Diocletian that the culprits were Christians, conspirators who had plotted with the eunuchs of the palace. An investigation was commissioned, but no responsible party was found. Executions followed anyway, and the palace eunuchs Dorotheus and Gorgonius were executed. One individual, Peter, was stripped, raised high, and scourged. Salt and vinegar were poured in his wounds, and he was slowly boiled over an open flame. The executions continued until at least April 24 303, when six individuals, including the bishop Anthimus, were decapitated. A second fire occurred sixteen days after the first. Galerius left the city for Rome, declaring Nicomedia unsafe. Diocletian would soon follow.
Although further persecutionary edicts followed, compelling the arrest of the Christian clergy and universal acts of sacrifice, the persecutionary edicts were ultimately unsuccessful; most Christians escaped punishment, and even pagans were generally unsympathetic to the persecution. The martyrs' sufferings strengthened the resolve of their fellow Christians. Constantius and Maximian did not apply the later persecutionary edicts, and left the Christians of the West unharmed. Galerius rescinded the edict in 311, announcing that the persecution had failed to bring Christians back to traditional religion. Within twenty-five years of the persecution's inauguration, the Christian emperor Constantine would rule the empire alone. He would reverse the consequences of the edicts, and return all confiscated property to Christians. Under Constantine's rule, Christianity would become the empire's preferred religion. Diocletian was demonized by his Christian successors: Lactantius intimated that Diocletian's ascendancy heralded the apocalypse, and in Serbian mythology, Diocletian is remembered as Dukljan, the adversary of God.
Diocletian entered the city of Rome in the early winter of 303. On November 20, he celebrated, with Maximian, the twentieth anniversary of his reign (vicennalia), the tenth anniversary of the Tetrarchy (decennalia), and a triumph for the war with Persia. Diocletian soon grew impatient with the city. It did not give enough deference to his supreme authority; it expected him to act the part of an aristocratic ruler, not a monarchic one. On December 20 303, Diocletian cut short his stay in Rome and left for the north. He did not even perform the ceremonies investing him with his ninth consulate; he did them in Ravenna on January 1 304 instead. There are suggestions in the Panegyrici Latini and Lactantius' account that Diocletian arranged plans for his and Maximian's future retirement of power in Rome. Maximian, according to these accounts, swore to uphold Diocletian's plan in a ceremony in the temple of Jupiter.
From Ravenna, Diocletian left for the Danube. There, possibly in Galerius' company, he took part in a campaign against the Carpi. He contracted a minor illness while on campaign, but his condition quickly worsened and he chose to travel in a litter. In the late summer he left for Nicomedia. On November 20, he appeared in public to dedicate the opening of the circus beside his palace. He collapsed soon after the ceremonies. Over the winter of 304–5 he kept within his palace at all times. Rumors alleging that Diocletian's death was merely being kept secret until Galerius could come to assume power spread through the city. On December 13, he seemed to have finally died. The city was sent into a mourning from which it was only retrieved by public declarations of his survival. When Diocletian reappeared in public on March 1 305, he was emaciated and barely recognizable.
Galerius arrived in the city later in March. According to Lactantius, he came armed with plans to reconstitute the Tetrarchy, force Diocletian to step down, and fill the imperial office with men compliant to his will. Through coercion and threats, he eventually convinced Diocletian to comply with his plan. Lactantius also claims that he had done the same to Maximian at Sirmium. On May 1 305, Diocletian called an assembly of his generals, traditional companion troops, and representatives from distant legions. They met at the same hill, out of Nicomedia, where Diocletian had been proclaimed emperor. In front of a statue of Jupiter, his patron deity, Diocletian addressed the crowd. With tears in his eyes, he told them of his weakness, his need for rest, and his will to resign. He declared that he needed to pass the duty of empire on to someone stronger. He thus became the first Roman emperor to voluntarily abdicate his title.
Most in the crowd believed they knew what would follow; Constantine and Maxentius, the only adult sons of a reigning emperor, men who long been preparing to succeed their fathers, would be granted the title of Caesar. Constantine had traveled through Palestine at the right hand of Diocletian, and was present at the palace in Nicomedia in 303 and 305. It is likely that Maxentius received the same treatment. In Lactantius' account, when Diocletian announced that he was to resign, the entire crowd turned to face Constantine. It was not to be: Severus and Maximin were declared Caesars. Maximin appeared and took Diocletian's robes. On the same day, Severus received his robes from Maximian in Milan. Constantius succeeded Maximian as Augustus of the West, but Constantine and Maxentius were entirely ignored in the transition of power. This did not bode well for the future security of the Tetrarchic system.
He lived on for three more years, spending his days in his palace gardens. He saw his Tetrarchic system implode, torn by the selfish ambitions of his successors. He heard of Maximian's third claim to the throne, his forced suicide, his damnatio memoriae. In his own palace, statues and portraits of his former companion emperor were torn down and destroyed. Deep in despair and illness, Diocletian may have committed suicide. He died on December 3 311.
Diocletian saw his work as that of a restorer, a figure of authority, whose duty it was to return the empire to peace, and recreate stability and justice where barbarian hordes had destroyed it. He arrogated, regimented and centralized political authority on a massive scale. In his policies, he enforced an imperial system of values on a diverse and sometimes unwilling provincial audience. In the imperial propaganda from the period, recent history is perverted and minimized in the service of the theme of the Tetrarchs as "restorers". Aurelian's achievements are ignored, the revolt of Carausius is backdated to the reign of Gallienus, and it is implied that the Tetrarchs engineered Aurelian's defeat of the Palmyrenes; the period between Gallienus and Diocletian is effectively erased. The history of the empire before the Tetrarchy is portrayed as a time of civil war, savage despotism, and imperial collapse. In those inscriptions that bear their names, Diocletian and his companions are referred to as "restorers of the whole world", men who succeeded in "defeating the nations of the barbarians, and confirming the tranquility of their world". Diocletian was written up as the "founder of eternal peace". The theme of restoration was conjoined to an emphasis on the uniqueness and accomplishments of the Tetrarchs themselves.
The cities where emperors lived frequently in this period—Milan, Trier, Arles, Sirmium, Serdica, Thessaloniki, Nicomedia, and Antioch—were treated as alternate imperial seats, to the exclusion of Rome and its senatorial elite. A new style of ceremony was developed, emphasizing the distinction of the emperor from all other persons. The quasi-republican ideals of Augustus' primus inter pares were abandoned for all but the Tetrarchs themselves. Diocletian took to wearing a gold crown and jewels, and forbade the use of purple cloth to all but the emperors. His subjects were required to prostrate themselves in his presence (adoratio); the most fortunate were allowed the privilege of kissing the hem of his robe (proskynesis, προσκύνησις). Circuses and basilicas were designed with to keep the face of the emperor perpetually in view, and always in a seat of authority. The emperor became a figure of transcendent authority, a man beyond the grip of the masses. His every appearance was stage-managed. This style of presentation was not new—many of its elements were first seen in the reigns of Aurelian and Severus—but it was only under the Tetrarchs that it was refined into an explicit system.
Altogether, Diocletian effected a large increase in the number of bureaucrats at the government's command; Lactantius was to claim that there were now more men using tax money than there were paying it. The historian Warren Treadgold estimates that under Diocletian the number of men in the civil service doubled from 15,000 to 30,000. The classicist Roger Bagnall, based on data produced by A.H.M. Jones, estimated that there was one bureaucrat for every 5–10,000 people. (By comparison, the ratio in twelfth-century China was one bureaucrat for every 15,000 people.)
For a more efficient collection of taxes and supplies, and to ease the enforcement of the law, Diocletian doubled the number of provinces from fifty to almost one hundred. The provinces were grouped into twelve dioceses, each governed by an appointed official called a vicarius, or "deputy of the praetorian prefects". Some of the provincial divisions required revision, and were modified either soon after 293 or early in the fourth century. The dissemination of imperial law to the provinces was facilitated under Diocletian's reign, because Diocletian's reform of the empire's provincial structure meant that there were now a greater number of governors (praesides) ruling over smaller regions and smaller populations. Diocletian's reforms shifted the governors' main function to that of the presiding official in the lower courts: whereas in the early empire military and judicial functions were the function of governor, and procurators had supervised taxation; under the new system vicarii and governors were responsible for justice and taxation, and a new class of duces ("dukes"), acting independently of the civil service, had military command. These dukes sometimes administered two or three of the new provinces created by Diocletian, and had forces ranging from two thousand to more than twenty thousand men. In addition to their roles as judges and tax collectors, governors were expected to maintain the postal service (cursus publicus) and ensure that town councils fulfilled their duties.
As with most emperors, much of Diocletian's daily routine rotated around legal affairs, responding to appeals and petitions, and delivering decisions. Rescripts, authoritative interpretations issued by the emperor in response to demands from disputants in both public and private cases, were a common duty of second- and third-century emperors. Diocletian was awash in paperwork, and was nearly incapable of delegating his duties. It would have been seen as a dereliction of duty to ignore them. Diocletian's praetorian prefects—Afranius Hannibalianus, Julius Asclepiodotus, and Flavius Constantius—aided in regulating the flow and presentation of such paperwork, but the deep legalism of Roman culture kept the workload heavy. Emperors in the forty years preceding Diocletian's reign had not managed these duties so effectively, and their output in attested rescripts is low. Diocletian, by contrast, was prodigious in his affairs: there are around 1,200 rescripts in his name still surviving, and these probably represent only a small portion of the total issue.
Under the governance of the jurists Gregorius, Aurelius Arcadius Charisius, and Hermogenianus, the imperial government began issuing official books of precedent, collecting and listing all the rescripts that had been issued from the reign of Hadrian (r. 117–38) to the reign of Diocletian. The Codex Gregorianus includes rescripts up to 292, which the Codex Hermogenianus updated with a comprehensive collection of rescripts issued by Diocletian in 293 and 294. The jurists themselves were generally conservative, and constantly looked to past Roman practice and theory for guidance. They were probably given a looser administrative structure than that imposed on the later compilers of the Codex Theodosianus (438) and Codex Justinianus (529). Their work lacked the rigid structuring of those later codes, and was not published in the name of the emperor, but in the names of its compilers. The compilers' codifications were a radical innovation, given the decentralized nature of the Roman legal system. There is a sharp increase in the number of edicts and rescripts produced under Diocletian's rule, a fact that has been read as evidence of the Diocletian's thoroughgoing effort to realign society on terms established by the imperial center.
After Diocletian's reform of the provinces, governors were often referred to by the name iudex, or judge. The governor became responsible for his decisions first to his immediate superiors, as well as to the more distant office of the emperor. It was most likely at this time that judicial records became verbatim accounts of what was said in trial, making it easier to determine bias or improper conduct on the part of the governor. With these records and the empire's universal right of appeal, imperial authorities probably had a great deal of power to enforce behavior standards for their judges. In spite of Diocletian's attempts at reform, the provincial restructuring was far from clear, especially when citizens appealed the decisions of their governors. Proconsuls, for example, were often both judges of first instance and appeal, and the governors of some provinces took appellant cases from their neighbors. It soon became impossible to avoid taking some cases to the emperor for arbitration and judgment. Diocletian's reign marks the end of the classical period of Roman law. Where Diocletian's system of rescripts shows an adherence to classical tradition, Constantine's law is full of Greek and eastern influences.
Lactantius criticized Diocletian for an excessive increase in troop sizes, declaring that "each of the four [Tetrarchs] strove to have a far larger number of troops than previous emperors had when they were governing the state alone". The fifth-century pagan Zosimus, by contrast, praised Diocletian for keeping troops on the borders, rather than keeping them in the cities, as Constantine was held to have done. Both these views had some truth to them, despite the biases of their authors: Diocletian and the Tetrarchs did greatly expand the army, and the growth was mostly in frontier regions, although it is difficult to establish the precise details of these shifts given the weakness of the sources. The army expanded to about 581,000 men from a 285 strength of 390,000 men. The growth was smaller in the East, which only expanded from 253,000 men to 311,000 men, most of whom manned the Persian frontier. The navy's forces increased from approximately 46,000 men to approximately 64,000 men.
Diocletian's increases in the size of the civil service and the military forces of his empire meant that the empire's tax burden would also increase, especially given how the military was the largest burden on the imperial budget. The proportion of the adult male population serving in the army increased from roughly 1 in 25 to 1 in 15, an increase judged excessive by some modern commentators. Official troop allowances were kept to low levels, and the mass of troops often resorted to extortion or the taking of civilian jobs. Arrears became the norm for most troops. Many were even given payment in kind in place of their salaries. Were he unable to pay for his enlarged army, there would likely be civil conflict, potentially open revolt. Diocletian was led to devise a new system of taxation.
Most taxes were due on each September 1, and levied from individual landowners by decuriones (decurions). These decurions, analogous to city councilors, were responsible for paying from their own pocket what they failed to collect from the populace. Diocletian's reforms also increased the number of financial officials in the provinces: more rationales and magistri privatae are attested under Diocletian's reign than before. These offices were to manage imperial properties and to supervise the collection of revenue. Despite the instability of the coinage, most taxes were either levied in or convertible into money. Rates shifted to take inflation into account. In 296, Diocletian issued an edict reforming census procedures. This edict introduced a general five-year census for the whole empire, replacing prior censuses that had operated at different speeds throughout the empire. The new censuses would keep up with changes in the values of capita and iuga. In the interests of securing a generally egalitarian tax system, Italy, which had long been exempt from taxes, was exempt no longer. Save for the city of Rome and a region extending one hundred miles in every direction from the city center (the Suburbicarian dioceses), Italy would now be taxed on the same level as any other province.
Diocletian's edicts emphasize the common liability of all taxpayers. Public records of all taxes were established to enhance the transparency of the operation, so that taxpayers would know exactly how much their neighbors paid. The position of decurion had long been an honor sought by wealthy aristocrats, but under Diocletian its tax-collecting requirements became much more rigorous. Decurions and the city treasury could be bankrupted if production figures fell. The effects of the new tax system were deeply felt: boundary-markers (necessary for tax administration) dating from the Tetrarchic period make relatively frequent appearances in Near-Eastern towns, even in remote country districts like Sakkaia in the northern Hauran. The Roman populace, long accustomed to irregular and ineffective tax collection, went through an uncomfortable period of adjustment to Diocletian's reforms. But even the lower classes were able to pay this burden. The common benefits of the new system were clear: taxes were predictable, regular, and fair, and the population was now free from fear. Citizens of the fourth century, safe behind the frontiers established and paid for by their taxes, no longer had to fear foreign occupation.
By the early 280s, market forces had created a stable exchange rate between gold and the copper antoninianus, more or less stabilizing commodity prices. The antoninianus, which had become the standard medium of exchange, was valued at one sixty-thousandth the value of a pound of gold. Inflation, however, remained a serious issue: In spite of attempts to wean the nation off metal currency by converting governmental taxes and salaries to annonary payments in kind, metal currency remained in wide circulation. In the wake of a brief period of re-inflation, Diocletian began a more comprehensive reform of the currency in 293. The new system consisted of five coins: the aureus/solidus, a gold coin weighing, like its predecessors, one-sixtieth of a pound; the argenteus, a coin weighing one ninety-sixth of a pound and containing ninety-five percent pure silver; the follis, sometimes referred to as the laureatus A, which is a copper coin with added silver struck at the rate of thirty-two to the pound; the radiatus, a small copper coin struck at the rate of 108 to the pound, with no added silver; and a coin known today as the laureatus B, a smaller copper coin struck at the rate of 192 to the pound. The state-assigned nominal values on these coins were set higher than their intrinsic worth, meaning that the state was issuing these coins at a loss. This practice could be maintained only by requisitioning precious metals from private citizens in exchange for state-minted coin (of a far lower value than the price of the precious metals requisitioned).
By 301, however, the system was in trouble, strained by a new bout of inflation. Diocletian therefore issued his Edict on Coinage, an act re-tariffing all debts so that the nummii, the most common coin in circulation, would be worth half as much. In the edict, preserved in an inscription from the city of Aphrodisias in Caria (near Geyre, Turkey), it was declared that all debts contracted before September 1 301 would be repaid at the old standards, while all debts contracted after September 1 would be repaid at the new standards. It appears that the edict was made in an attempt to preserve the current price of gold and to keep the empire's coinage on silver, Rome's traditional metal currency. This edict risked giving further momentum to inflationary trends, as had happened after Aurelian's currency reforms. Soon the Tetrarchic government could see no better solution to its monetary woes than a series of price freezes.
The Edict on Maximum Prices (Edictum De Pretiis Rerum Venalium in Latin) was issued two to three months after the coinage edict, somewhere between November 20 and December 10 301. It survives in many different versions, written on wood, papyrus, and stone. It is the best-preserved Latin inscription surviving from the Greek East. In the edict, Diocletian declared that the current pricing crisis resulted from the unchecked greed of merchants, and had resulted in turmoil for the mass of common citizens. The language of the edict calls on the people's memory of their benevolent leaders, and exhorts them to enforce the provisions of the edict, and thereby restore perfection to the world. The edict goes on to list in detail over one thousand goods and accompanying retail prices not to be exceeded. Penalties are laid out for various pricing transgressions.
In the most basic terms, the edict was ignorant of the law of supply and demand; it ignored the fact that prices might vary from region to region, or according to product availability, and it ignored the impact of transportation costs in the retail pricing of goods. In the judgment of the historian David Potter, the edict was "an act of economic lunacy". Inflation, speculation, and monetary instability continued, and a black market arose to trade in goods forced out of official markets. The edict's penalties were applied unevenly across the empire (some scholars believe they were applied only in Diocletian's domains), widely resisted, and eventually dropped, perhaps within a year of the edict's issue. Lactantius has written of the perverse accompaniments to the edict; of goods withdrawn from the market, of brawls over minute variations in price, of the deaths that came when its provisions were enforced. His account may be true, but it seems to modern historians exaggerated and hyperbolic, and the impact of the law is recorded in no other ancient source.
Constantine abandoned Diocletian's aim of preserving a stable silver coinage, and minted instead a new gold solidus. Diocletian's paganism was repudiated in favor of an imperially sponsored Christianity; his attempts at controlling prices ignored. But even Christianity became tied to the state structure of the Roman Empire in an autocratic way; Constantine claimed for himself the same close relationship with the Christian God as Diocletian had claimed with Jupiter. Most importantly, Diocletian's tax system was preserved and tightened. Aided by the new state machinery introduced by Diocletian, the Byzantine Empire would last for over one thousand years after his death.