A Roman emperor (full name, Valerius Diocletianus; also called Diocles) from 20 November 284 to May 305. He was born in 245 of humble parents in the province of Dalmatia. He enlisted in the army and gained administrative experience in minor posts in Gaul under Aurelian (270-275), and in 282 became governor of Moesia under Carus. The next year he was made commander of the emperor’s bodyguard, and in that capacity accompanied Carus on his Persian campaign.

Carus died on the campaign (8 September 283), and on the return march of the Roman army from Persia in 284, Diocles began his rise to eminence. Carus’s younger son, Numerian, died in suspicious circumstances in the autumn of 284. Diocles was appointed emperor by a council of officers and avenged his predecessor’s death by killing the praetorian prefect, Aper, who was suspected of the murder (17 November 284). Three days later Diocles was formally proclaimed emperor at Nicomedia in Bithynia.

Meantime, Carus’s elder son, Carinus, had proved himself incapable of governing the western provinces of the empire. Diocles met his army at Horrea Margus in Pannonia in March 285. In the ensuing battle Carinus prevailed, but Diocles was rescued from the consequences of defeat through the murder of Carinus by an officer whose wife he had seduced. The leaderless army then accepted Diocles as sole emperor.

At this moment there was no reason to believe that Diocletian, as he now styled himself, would last any longer than his militarily more able predecessors. He was, however, to rule for twenty-one years, to abdicate, and then live for almost a decade in retirement in the majestic miniature praetorium that he had built for himself at Spalato (Split) on the Adriatic coast.

The reasons for the success of Diocletian were his ability to delegate responsibilities to trusted subordinates; to anchor his administrative reforms firmly on principles of government that recalled the virtues, real or imagined, of the Roman past; and to give his system of government a traditional religious basis through acceptance of the Roman Jupiter and Hercules as its patrons.

He was an able and respected, if not particularly beloved, figure, a vir rei publicae necessarius, as he was called by the writer (or writers) of the Scriptores historiae Augustae a ruler required by the times.

Diocletian quickly followed the example of Carus by delegating his authority in the West. In March 286 he elevated an old comrade in arms, Maximian, to the rank of Augustus and dispatched him to Gaul to deal with an uprising of peasants (Bagaudae) against the Gallic landowners and imperial authority (Aurelius Victor, Liber de Caesaribus 39.17). Maximian was successful, as he was later in three campaigns against the more formidable Kabyles in North Africa (287-289). Meanwhile, Diocletian was victorious in a campaign against Saracen Arabs threatening Syria, and in 292 against rebels in Coptos and in Upper Egypt. The cause of the rebellion is not known. The only reverse suffered by the emperors in this first decade of their rule was the revolt of Carausius, Maximian’s commander of the fleet in the English Channel, in 287. He proclaimed himself emperor, but throughout his rule of six years in Britain (he was murdered in 293) he sought in vain to win acceptance as a “third emperor” rather than attempt to overthrow his “colleagues.”

Carausius’ success in maintaining himself may have contributed to a further delegation of power by the two emperors. In March 293 each nominated a or Caesar. Diocletian chose Galerius, and Maximian chose a proven administrator, Constantius. To cement mutual loyalties, marriage contracts bound members of the tetrarchy together, and the religious element was placed to the fore in Diocletian and Galerius’ assuming the style “Iovii” while Maximian and Constantius were “Herculii” (Seston, p. 97), able lieutenants of their seniors in the hierarchy as Hercules was to Jupiter in the hierarchy of the gods. To the imperial biographers (or their sources) the emperors were “courageous and wise, benign and open-handed, concerned for the welfare of the state, respectful to the Senate, friends of the people, serious-minded and pious toward the gods” (Scriptores historiae Augustae, Carus and Carinus XVIII.4).

Measures to restore the defenses and administration of the empire evolved slowly, as if they were responses to situations rather than the product of overall plans. The army, amounting to thirty-six legions under the Severi (193-235), was slowly increased until about double the effectives were under arms. Diocletian’s policy was defensive. The fifth-century historian Zosimus wrote, “By the foresight of Diocletian, the frontiers of the Roman Empire were everywhere studded with cities and forts and towers . . . and the whole army was stationed along them so that it was impossible for the barbarians to breakthrough, as the attackers were everywhere withstood by an opposing force” (Historia nova II.34).

There is plenty of archaeological evidence from Syria, North Africa, and Britain, to name three provinces, to demonstrate the truth of this. Diocletian’s concern for frontier defense had one effect on Egypt: the Dodekaschoenos, the area attributed to the direct governance of the goddess Isis, south of Aswan, was given up and the frontier brought back to the First Cataract. Defense against the marauding Blemmyes (see BEJA TRIBES) was entrusted henceforth to the friendly kingdom of NOBATIA.

Provincial reorganization followed the slow, deliberate pattern that had applied to the army. In the previous thirty years too many provincial governors had sought supreme power in the empire. Gradually the numbers of provinces and their governors was increased from forty-three to over one hundred. The reorganization affected Egypt as it did other areas. The Thebaid was from the unitary province of Aegyptius before 302, and from Libya before 308. The remainder of Egypt was destined to be subdivided into two further provinces, Iovia and Herculia, in 313.

New provinces entailed new provincial organization and a revised system of taxation and coinage. Throughout the empire taxation was now based on a mixture of a poll tax (capitatio), at first probably applied only to the rural population and later including town dwellers (Lactantius De mortibus xxiii.7), and a tax on land, based on ideal and arbitary units called iuga, graded according to official assessments of productivity. In Egypt the assessment extended to boys aged twelve (Jones, p. 51) and the urban poll tax was in force by 301 (Jones, p. 63). The land tax continued to be levied on the traditional measure of acreage, the aroura, of arable vineyards and olive trees.

To match these fiscal changes, the coinage was drastically reformed. The massive inflation that had destroyed the value of the antoninianus had also destroyed the value of the local urban and provincial currencies that had been one of the sources of pride in the city-states, especially in the eastern Mediterranean. Even the Alexandrian tetradrachm had become reduced to a small disk of alloy of a circumference no greater than one centimeter.

In 295-296, perhaps influenced by Carausius’ currency reform in Britain, Diocletian instituted an empirewide currency with gold, silver, and silver-covered pieces, the last of these minted in the tens of thousands at mints from Alexandria to Lyons and bearing the same inscription on the reverse: Genio Populi Romani (to the genius of the Roman people). Jupiter was shown standing and holding a sacrificial dish in his hand. Roman religion was never far from the emperor’s mind.

Religious tradition and uniformity were foremost among both the motives and the consequences of Diocletian’s reorganization of the empire. Both are in evidence in the legal decisions of the period. Justinian’s code and minor collections preserve about 1,300 constitutions of Diocletian that range from simple matters of private law to important enactments concerned with social customs and religion (Jones, 1964, p. 37). The spirit of the emperor’s legislation can be understood from the horror that he expressed when made aware of the custom in Egypt of marriage between brother and sister.

In his decree De nuptiis (c. 295) he declared this was contrary to “the discipline of our times,” “barbarian savagery,” and “displeasing to the immortal gods,” who would favor the empire, if the people would perceive how “all under our sway were living lives of piety and religious observance in quietude and chastity” (Codex Gregorianus v, Mosaicarum et Romanorum legum collectio vi.4, ed. Riccobono, Vol. 2, pp. 558-60). Roman religious observances were to have universal application.

Another imperial rescript, addressed to Julianus, proconsul of Africa, on 31 March 297 (or 302), foreshadowed Diocletian’s later edicts against the Christians. This time the enemy was the Manichaeans. Issued probably at the outset of the war with Persia, the edict combines anger at the proselytizing activities of what was considered a religion serving the interests of the enemy with resolve to defend the traditional religion of Rome. “The wickedness of attempting to undo past tradition” required the emperor to act with great zeal “to punish the obstinacy of the perverted mentality of these most evil men.” The leaders of the sect and their books were to be burned. Other adherents were to be put to death by beheading (Mosaicarum et Romanorum legum collectio v.4, Vol. 2, pp. 580-81). Other dissidents could expect small mercy.

The attempt to reassert past values may have influenced another of Diocletian’s policies: the restoration of the cities with their public buildings, and not least their temples. All over the empire the era of the tetrarchy witnessed a great effort to breathe new life into the cities. Inscriptions preserve evidence for the restoration of temples in eight North African towns, and public works are attested in many others.

However retrograde and oppressive in their effects some of these measures were, there is no denying the idealism that inspired even the most futile. The Edict of Prices of 301 was prefaced by the provincial governor of Caria, Fulvius Asticus, with the statement “This is also a sign of the divine foresight [of the emperor], namely, that a fair and fixed price should be laid down for everything.” The aim was a plentiful livelihood for all and the curtailing of the greed of a few (see Crawford and Reynolds, 1975). Similarly, the census of 297 that preceded the institution of the new order of taxation was justified by the prefect of Egypt, Aristius Optatus, on the ground that to date “some taxpayers are undercharged and others overburdened” (Boak and Youtie, 1960, no. 1; Seston, 1946, pp. 283-84).

Diocletian’s measures of reform were, however, immensely costly. The buildings alone, not least the new imperial palaces, must have consumed vast resources in manpower and wealth to yield little productive value. Gradually, society was reduced to a siege economy in which people and organizations were rigidly stratified, and social mobility was reduced to a minimum. Apart from officials the most favored were “the honorable soldiers,” for whom annona (taxation in kind) must be provided (Oxyrhynchus Papyrus 1543, dated to A.D. 299); the least considered were the peasants, who by now were practically bound to the soil. In between were the urban middle classes, once the backbone of the empire but now increasingly anxious to avoid their traditional responsibilities of governing the cities and ensuring that these met the quota of taxes imposed on them.

Though many benefited from the emperor’s measures, there was also bitter criticism, especially from the Christians, of whom the writer Lactantius, who spent ten years (293-303) as professor of (Latin) rhetoric at Diocletian’s court at Nicomedia, was the most articulate. In his pamphlet On the Deaths of the Persecutors (De mortibus persecutorum), written about 315, after the victory of Constantine, practically every one of Diocletian’s major reforms was attacked. The reduction in the number of provinces was “chopping the provinces into slices” (vii.4). The tightening of administrative control by diminishing the areas for which individual officials were responsible was criticized as producing more officials and more departments in each district, as was usual in cities (vii.4). Even more vitriolic was his denunciation of the census: “Only beggars from whom nothing could be exacted escaped the measures of this pious man [Diocletian]. Neither age nor infirmity was accepted as an excuse. Old men and the sick were forced to appear [and register]. The age of each was estimated, years being added to that of children and deducted from that of the aged” (xxiii.4). The number of official recipients exceeded that of those paying. The country folk were oppressed and impoverished in particular, and the extravagant building program added to the universal distress (xxiii.7).

Exaggeration, perhaps, but as Eutropius (Breviarium ix.23) pointed out, taxation was oppressive, and not least in Egypt, where a new revolt broke out in 296. This time the rebels proclaimed a rival emperor, Domitius Celsus, with an effective field commander, Aurelius Achilleus. Diocletian was compelled to retake Alexandria from the rebels through the winter and into the spring of 296/297. Henceforth he had little love for the Egyptians. This episode unintentionally led to the greatest crisis of his reign: the final effort to destroy organized Christianity in the Great Persecution of 303-312.

The revolt in Egypt gave the Persians the chance to expel the pro-Roman king of Armenia, Tiradates, and establish their own candidate on the throne, thus provoking a war with Rome. In the first campaign during 297, Galerius, Diocletian’s Caesar, was defeated; but in the spring of 298, reinforced by legions from the Danube and stung by Diocletian’s unconcealed displeasure, he won a decisive victory over the Persian king Narses. The latter was forced to surrender five small provinces north of the upper Tigris to the empire, amounting to a protectorate over Armenia, where he acknowledged Roman interests. Galerius returned in triumph (May 298). There is no reason to disbelieve the testimony of Lactantius and Eusebius of Caeserea that henceforth the situation gradually worsened for the Christians (Eusebius Chronica ad annum 302). Not only was Galerius strongly anti-Christian (Lactantius De mortibus 9), but the Christian church now stood out as the one great organization that was outside the uniform structure that Diocletian had imposed on the empire.

“Little by little persecution against us began,” wrote Eusebius (Chronica ad annum 302). Diocletian moved cautiously. At first, only Christian soldiers were forced to resign from imperial service, but by 302 the crisis point was approaching. Counsel was held with Galerius and senior officials, prominent among whom was Sossianus Hierocles, governor of Bithynia. They advised action. A visit in the winter of that year to the oracle of Apollo at Didyma near Miletus brought a similar result, the oracle replying that “an enemy of the divine religion” (i.e., the Christians) prevented him from uttering (De mortibus xi.7). The die was now cast, Diocletian’s restraint being confined to his insistence that no blood should be spilled.

The feast of Terminalia, 23 February, was selected as the day that would set the term for the Christian faith. On that day, soldiers set about destroying the cathedral of Nicomedia, which stood in full view of the imperial palace. Diocletian signed a decree ordering the Christian sacred books to be handed over for burning and the churches to be destroyed. Christians were to be dismissed from public office. In civil life Christians of the upper classes, the honestiores, were to lose their privileges; and Christians could no longer act as accusers in cases of personal injury, adultery, and theft. Only their lives were spared.

In Egypt the persecution caused consternation among the Christian leaders. Peter (300-311) fled Alexandria to Oxyrhynchus, and thence probably from Egypt. One of the leading intellectuals, the presbyter Pierius, whose fame as a theologian and ascetic had earned him the title “Origen the Younger,” seems to have conformed. So far as the church of Alexandria was concerned, he thereby disgraced himself. Many Christians, however, sacrificed to the Roman with him. In the countryside, churches were destroyed or dismantled, but in general the persecution caused more inconvenience than suffering to Christians (Oxyrhynchus Papyrus 2673).

The second and third edicts of persecution, in the summer and autumn of 303, were aimed at enforcing the conformity of the clergy, and a great sense of triumph was felt when they succeeded. However, up to the time Diocletian celebrated his vicennalia at Rome on 20 November 303, only those who deliberately defied the authorities or otherwise rushed to a martyr’s death had lost their lives (thus Eusebius, Martyrs of Palestine i.1, concerning Procopius of Gaza, executed on 7 June 303). In the winter of 303/304, however, Diocletian became ill from a lingering malady, perhaps malaria, and power passed to Galerius. Up to then the persecution had affected “only the presidents of the churches” (Martyrs of Palestine iii.1) or at least only prominent Christians, but the fourth edict that Galerius promulgated in the spring of 304 required all to sacrifice to the on pain of punishment, including death. One notable martyr, Phileas, of Tmuis, was arrested probably at this time. Even so, Egypt does not seem to have suffered more heavily at this stage than other parts of the empire. One reads in the account of the origins of the Melitian schism (preserved in Epiphanius Panarion 68.1) of and monks imprisoned but not executed. The effect was that all Coptic Christians now found themselves drawn into a situation of opposition to the imperial authorities. The many martyrdoms recorded in Eusebius belong, however, to the reign of Maximin (305-313).

Diocletian recovered sufficiently to resume authority for a short time in the spring of 305. But he had decided, perhaps while in Italy, to abdicate and had persuaded his colleague Maximian to follow his example. According to Aurelius Victor, writing half a century after the event, he may have been plagued with forebodings over the future of the empire, or he may have yielded to pressure by Galerius. In any event, on 1 May 305, before a great parade of troops at Nicomedia, Diocletian laid aside the purple and stepped down from the dais a private citizen, the only Roman emperor ever to retire.

Diocletian was one of the great conservative reformers of history—the more effective, perhaps, because his reforms were in the nature of responses to situations rather than the result of long- preconceived policies. His reign saw a flowering of a new but authentically Roman form of art, particularly the imperial portraiture on the coinage, and architecture such as the Arch of Galerius at Salonika, as well as the emphasis on traditional religious and ethical values. The onslaught against the Christians, though it surprised contemporaries who saw it as an “act of madness” (Eusebius De vita Constantini 1.13), can be understood in retrospect as an almost inevitable result of the emperor’s drive for uniformity throughout the empire. The two serious revolts in Egypt during his reign indicate, however, a deep resentment against the tetrarchy and its rule. With Christianity becoming increasingly strong, the emperor’s initiation of the policy of persecution, and the involvement by 304 of the whole Egyptian Christian population, was enough to cause the Copts to brand him the supreme persecutor, and to date the ERA OF THE MARTYRS from his accession. It was not an just stigma.


  • No full-scale study of Diocletian exists because W. Seston did not write the projected second volume of Dioclétien et la Tétrarchie (Paris, 1946), but a full account of the reign will be found in the Cambridge Ancient History, Vol. 12, chaps. 9-11, 19 (Cambridge, 1939); in A. M. M. Jones, The Later Roman Empire, chap. 2 (Oxford, 1964); and in W. Ensslin, “Valerius Diocletianus,” in Pauly-Wissowa, ser. 2, Vol. 2, cols. 2419-2495 (Stuttgart, 1948).
  • See also D. Barnes, Constantine and Eusebius (Cambridge, Mass., 1981), and his companion volume, The New Empire of Diocletian and Constantine (Cambridge, Mass., 1981).
  • W. H. C. Frend, Martyrdom and Persecution in the Early Church (Oxford, 1965; and 2nd ed., Grand Rapids, Mich., 1981), chap. 15, is useful on the emperor’s religious policy; see also G. E. M. de Ste. Croix, “Aspects of the Great Persecution,” Harvard Theological Review 47 (1954):75-131; and J. Moreau, ed., Lactance. De la mort des persécuteurs, 2 vols. Sources Chrétiennes 39 (Paris, 1954).
  • On Diocletian’s abdication, see G. S. R. Thomas, “L’abdication de Dioclétien,” Byzantion 43 (1973):220-24.
  • On the public works undertaken in Diocletian’s reign, see C. R. van Sickle, “The Public Works in Africa in the Reign of Diocletian,” Classical Philology 25 (1930):173-79.
  • On the Edict of Prices see M. H. Crawford and Joyce Reynolds, “The Publication of the Prices Edict, a New Inscription from Aezani,” Journal of Roman Studies 65 (1975):160-64, and K. T. Erim and Joyce Reynolds, “The Aphrodisias Copy of Diocletian’s Edict on Maximus Prices,” Journal of Roman Studies 63 (1973):99-110.
  • For the martyrdom of Phileas, see H. Musurillo, ed., The Acts of the Christian Martyrs, pp. 328-353 (Oxford, 1972).