Ancient History & Civilisation

The Age of Diocletian and Constantine

The formation of the late Roman state extended over half a century, from Diocletian's seizure of power in 284 until the death of Constantine in 337. The entire period witnessed almost continuous warfare against internal and external enemies. There were struggles in the West against the Germanic tribes along the Rhine frontier and in Britain against the usurper Carausius. In the East there were revolts in Egypt and a major war with Persia, which culminated in a favorable peace treaty in 299. In the years that followed the victory against the Sassanians, Galerius also secured the Danube frontier.

As the threat of war emerged on all fronts, new imperial residences developed in the frontier regions of the empire. Maximianus was usually based at Milan or Aquileia in northern Italy, relinquishing his former headquarters at Trier to Constantius after 293. Diocletian and Galerius held court at Sirmium, Serdica, and Thessalonica in their European provinces, and at Nicomedia and Antioch in the East. These strategic and administrative centers contained palaces to accommodate the imperial court, garrison quarters for troops accompanying the emperors, and amphitheaters and circuses for shows and imperial ceremonials.14 Formal public ceremonies were an important ingredient of imperial power. The Latin historians noted that Diocletian increased the distance between the emperor and his subjects by requiring them to prostrate themselves in his presence. Modern commentators have sometimes interpreted this as a move to orientalize the monarchy.15 This habit at the imperial court can be traced back to the Severan period, but it is evident that under the tetrarchs such practices evolved into a much stricter court ceremonial, which deliberately increased the literal and metaphorical distance between the rulers and their subjects.16

The imperial residences became showplaces for Roman power and the most important locations for representing imperial culture. Panegyric speeches, such as the ones for Maximianus, simultaneously expounded the emperors' virtues and achievements and proclaimed the loyalty and devotion of their subjects. The occasions chosen were the five- or ten-year anniversaries of the ruler's term of office, their birthdays, or the successful conclusions of campaigns. They lauded the generic imperial virtues of courage, strength, foresight, and mercy, and hailed specific achievements, notably successful campaigns. They offered speakers the opportunity to add personal thanks to the rulers for offices they had been given, or to ask for future favors, particularly for the cities of Gaul. The message of the speeches is interwoven with religious propaganda and ideology. This is strikingly evident in the second panegyric for Maximianus of 291, in which the speaker developed at length the equation of Diocletian with Jupiter and Maximianus with Hercules, which had led the emperors to adopt the names Iovius and Herculius respectively.17 There is no doubt that the themes covered in the panegyrics were approved by the emperors themselves, at least in outline. Sometimes their wishes were explicit, as in the instance where Maximianus had charged the orator of 289 to pass quickly over his suppression of the Bagaudae. But in most cases the choice of topics will have been evident to all parties.

The ideas and style which suffused the panegyrics were also a dominant influence on other media of imperial self-presentation. Key political slogans and images became ubiquitous and were disseminated by coin types. Again the allusions might be generic, for instance to the VIRTUS and CONCORDIA AUGUSTORUM, or to the FELICITAS TEMPORUM, or they might refer to specific occasions and events. The coins also contain a full repertoire of imperial portrait types. Since Augustus, Roman rulers had used their own image to project the main moral and political characteristics of their reigns in a visual medium. The tetrarchs developed stern and vigilant portraits; square jawed, wide eyed, with the cropped hair and stubble beards of campaigning soldiers. In a ground-breaking study of the imperial portraiture of this period, R. R. R. Smith argues that these images embodied a radical new imperial idea and style. The visual record emphasized two features above all; the collegiality of the emperors, and their moral fundamentalism. Collegiality is expressed most famously in the multiple portraits of the four rulers, carved in porphyry which had been extracted from the imperial quarries in Egypt, clasping one another in an embrace of soldierly solidarity. Moral severity radiates from their harsh and unsmiling gaze (Plate 3.1).18 Official propaganda represented the tetrarchy as a united team of two senior and two junior members. At the same time it was acknowledged that Diocletian was the dominant member of the group. The potential strains as well as the reality of the relationship were well caught by the later emperor Julian, in his satirical essay on the Caesars, as he describes the tetrarchs entering the banquet of the gods:

Diocletian led the procession in his pomp, bringing with him the two Maximianuses and my grandfather Constantius. These held one another by the hands, and did not walk in line with him but they surrounded him like a sort of dancing troupe. They were like bodyguards, wanting to run out in front of him, but he kept preventing them, for he did not want to claim more than they in any way.19


Plate 3.1    The four rulers of the first tetrarchy. This statue made from porphyry, the hard purple granite of the imperial quarries in Egypt, was probably originally erected at Nicomedia, Diocletian's capital. It was transported and displayed at Constantinople, where it was popularly known as the Philadelphion, “brotherly friendship” (see p. 339). After the sack of Constantinople by the crusaders in 1204 it was taken to Venice, where it now stands at the corner of St Mark's cathedral (© Stefano Politi Markovina/Alamy)

Inscriptions focused the moral language of the panegyrics into lapidary formulae. Apart from dedications to the piety, courage, justice, and concord of the emperors, imperial edicts were enveloped in a wash of moralizing and propagandistic rhetoric. The obscure, but grandiloquent opening sentences of the famous price edict provide a good example:

Public honour, Roman dignity and Roman majesty require that the good fortune of our state be administered in a trustworthy manner and properly adorned. Alongside the immortal gods it is right to congratulate the state by recalling the wars that we have successfully fought, at a moment when the world is in a tranquil condition, placed in the lap of deepest calm thanks to the benefits of peace, for which labour has been expended with copious sweat. Thus we, who by kind favour of the gods have repressed the seething plunder previously inflicted by barbarian nations by slaughtering those people themselves, have reinforced the calm which has been established for all time with the necessary defences of justice. (ILS 642)

The passage emphasizes the effort that had been required to achieve this state of blessed tranquility, and the god whose endeavors had inspired and stood behind the emperors was indisputably Hercules.

A variety of propagandistic media projected the ideology of the tetrarchic rulers, and justified the power of the reigning emperors within the Roman world. Their purpose was not missionary, to win over new supporters, but was to create a sense of moral and political purpose. They envisaged no opposition or alternative to the emperors' authority, but were addressed to the loyal mass of imperial subjects.

Relief sculpture on official buildings commemorated imperial victories. However, these were portrayed as a precursor of the peace and justice that the warrior emperors had secured for their people. The sculptured panels of the victory arch at Thessalonica, probably erected between 303 and 305, celebrated Galerius' triumph over the Persians. The centerpiece was a panel depicting the two Augusti enthroned above two symbolic figures that may represent heaven and earth. They are flanked by the standing figures of their two Caesars in the act of raising two female figures to their feet. These doubtless represent the subject regions of the empire. Behind and around this scene stand the gods, protecting and supporting the empire's rulers.20

The core political program of the tetrarchy was promoted in the ceremonies which Diocletian held in Rome in 303 to commemorate the ten-year anniversary of the creation of the tetrarchy. A relief on the arch of Constantine, completed in 315, depicts the later emperor delivering a speech from the rostra in the Roman forum, amidst a gathering of magistrates and military officers, in front of a five-columned monument (Plate 9.1). This had been erected for the celebrations of 303. Two of the five inscribed and sculpted bases of these columns bore inscriptions which hailed the successful outcome of ten years of rule by the Caesars, and twenty years of the Augusti, Caesarum decennalia feliciter; vicennalia imperatorum. The base for the Caesars, which is still extant, depicts battle trophies on either side of the inscription, and shows on its other three sides scenes of the Caesars completing a sacrifice, a procession of armed soldiers and civilians in togas, and the combined sacrifice of ox, sheep, and pig, which was offered to the war god Mars. The largest column bore a statue of Jupiter, the others carried images which depicted the geniuses of the two Augusti and the two Caesars. This presented the essence of tetrarchic rule, which had brought order and peace to the Roman world under the religious authority of the supreme god Jupiter.21

Such propaganda was not confined to the main imperial residences. The tetrarchs made enormous efforts to project the image of the revived Roman state throughout the provinces. Architectural monuments were a favored medium. In several cities of Syria and Egypt existing buildings were demolished and the central civic squares were surgically enlarged to accommodate a new building type, the tetrakionia, the “four columns.” These comprised rectangular groups of four high podium bases, each in turn surmounted by four columns and baldachin roofs. These podia supported over-life-size statues of the tetrarchs, identified by dedicatory Latin inscriptions. These monuments served no practical function but literally thrust the presence of the ruling college into the urban communities of the eastern provinces.22

Another decisive innovation of the tetrarchic period was the use of Latin for all edicts published by the emperors, in the eastern as well as the western parts of the empire.23 The famous edict which set maximum prices for goods and services, as a means of controlling military costs, is exclusively known from copies set up in the eastern provinces, but in every case the text was carved in Latin, a language that few of the local inhabitants would have been able to understand. Latin was the language used for the imperial edicts which authorized measures against the Christians. Eusebius, who preserves the text of several of these documents, points out in these cases that his own versions are translations of the originals.

Diocletian was not only concerned with the projection of monarchic power but with measures of real substance. The first systematic attempts to codify Roman law, in the form of the Gregorian and Hermogenian codes, date to the time of Diocletian. Although these are not explicitly known to be the result of an imperial initiative, they clearly foreshadow the great codification of Roman law in the fifth and sixth centuries under Theodosius II and Justinian. The Gregorian Code, published around 292, consisted of some sixteen books, which gathered imperial legal rulings issued since the mid-second century, arranged by topic. The Hermogenian Code, published in 295, seems to have been a supplement to this, compiled by Aurelius Hermogenianus, the author also of a six-book digest of Roman civil law, who later held the office of praetorian prefect. Both collections were evidently designed as guidance for governors and other imperial officials, and for the lawyers on their staffs.24 But they also symbolized the intention of the tetrarchs to re-forge the empire into a secure and unified political structure, upheld by a framework of law and justice. Systematic publication of the rulings of the emperors, and hence of the laws of Rome, was one of the major institutional developments of the late empire.25

In 296 the tetrarchs reformed the procedures of the Roman census, replacing the irregular periodic census held in the provinces with regular five-year cycles. This was matched by a comparable attempt to set a uniform measure for the units of tax assessment, the caput and the iugum. The whole idea is set out in an edict by the prefect Aurelius Optatus, which introduced these measures to Egypt in 297:

The levy on each aroura according to the classification of the land, and the levy on each head of the peasantry, and from which age to which, may be accurately known from the recently issued divine edict and attached schedule, copies of which I have prefaced for promulgation with this edict of mine. Accordingly, seeing that in this too they have received the greatest benefaction, the provincials should make it their business in conformity with the divinely issued regulations to pay their taxes with all speed and by no means wait for the compulsion of the collector, for it is proper to fulfill most zealously and scrupulously all the loyal obligation, and if anyone should be revealed to have done otherwise after such bounty, he will risk punishment. (P. Cairo Isidore 1, trans. Lewis and Reinhold, Roman Civilization 2, 419)

This highly unpopular attempt to introduce more stringent tax collection led to resistance, which is reflected in Lactantius' On the Deaths of the Persecutors. It was followed by other measures to regulate the monetary economy. A currency edict of September 301 re-tariffed the imperial coinage at twice its previous face value, an attempt doubtless to keep pace with inflation. Two months later the edict of maximum prices was intended to cap rising costs and prevent avaricious profiteering. The consumers that the emperors most wanted to protect were not the generality of their subjects, but soldiers. It appears, however, that prices were in fact pegged at a level below market rates and were therefore unsustainable. The experiment collapsed almost at once amid general rancor, reported by Lactantius: “there was much blood shed over small and cheap things, nothing went on sale and price increased all the worse, until the law was abandoned after many deaths” (On the Deaths of the Persecutors 7.6–7).

In May 305, in accordance with a long-planned intention, Diocletian dissolved the first tetrarchy. He and Maximianus retired from office, and their Caesars Galerius and Constantius were promoted to Augusti in their places. Two new Caesars were nominated to the vacancies, Galerius Valerius Maximinus, the son of Galerius' sister, and Fl. Valerius Severus, whose relationship to the other members of the ruling college is uncertain. The new arrangements did not cater for the ambitions of Constantine and Maxentius, the sons of Constantius and Maximianus respectively, and a civil war ensued. This was not resolved until Diocletian was called from retirement to convene a conference at Carnuntum in Pannonia, which created a new tetrarchy in November 308. Galerius, Maximinus, Constantine, and Licinius, who was a protégé of Galerius, became the new rulers, with Galerius and Licinius as the official Augusti, and Maximinus and Constantine as the Caesars. The latter pair demanded and were given the rank of Augusti soon afterwards. Diocletian and Maximianus were confirmed in retirement, and Maxentius was again sidelined.

The conference at Carnuntum also produced one of the latest documents which illustrates the religious and political ideals of the original tetrarchy, an inscription which commemorates the building of a Mithraeum by the rulers:

The most religious Jovian and Herculian Emperors and Caesars restored the sanctuary for the unconquered sun god Mithras, the promoter of their empire. (ILS 659)

This text combined the Jupiter–Hercules theology, which Diocletian had developed to represent the politico-religious aspirations of the tetrarchy, with another central strand of late Roman imperial religion, the worship of the unconquered sun, Sol Invictus, who was fused, as often in this period, with Mithras, who was especially popular in military contexts.

Galerius and Maximinus now withdrew from the theater of civil war to the East, basing themselves at Thessalonica and Antioch respectively, while Licinius remained in Illyricum at Sirmium and Constantine in Gaul at Trier (Plate 3.2). However, the fundamental instability due to Maxentius' claims was still not removed. Maximianus retired to southern Gaul, while Maxentius himself, although not formally acknowledged by the tetrarchic college, established himself as Augustus in Italy, Rome and North Africa.


Plate 3.2    The Imperial Bath House at Trier, the empire's northern capital in the fourth century, which was for long periods the residence of the emperors Constantius, Constantine, Constans, Valentinian, and Gratian (S. Mitchell)

In 310 Constantine moved against Maximianus, who had once again claimed imperial power, and forced him to commit suicide near Massilia. Galerius died in May 311, leaving the empire ruled by a triumvirate of Augusti: Licinius, Constantine, and Maximinus. In 312 Licinius and Constantine converged on Maxentius. Constantine delivered the decisive blow. After crossing the Alps, and winning over most of the cities of northern Italy, Constantine defeated the bulk of Maxentius' forces at a battle outside Verona (Pan. Lat. XII [IX] 5–13; [X] 17, 21–24). He was now free to march on Rome, and delivered the coup de grâce on the city's doorstep at the battle of the Milvian bridge on October 28, 312. Maxentius himself perished in the waters of the Tiber. The Senate recognized Constantine as the senior Augustus, and he made a pact with Licinius at Milan in February 313, which was concluded by the marriage of Constantine's sister, Constantia, to his fellow emperor. After the death of Galerius in May 311 Maximinus, still officially Augustus in the East, took control of Asia Minor and occupied the palace at Nicomedia. In 313 he launched an invasion of Licinius' territory, but was defeated in a battle at Adrianople, fled east across Anatolia, and committed suicide in Tarsus in the summer of that year (Lactantius, On the Deaths of the Persecutors, 45–49).

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