Rome: Diocletian Tetrarchy (293-305): Diocletian, Maximian

53 *DIOCLETIAN (67; r.284-305; d.312) (all→E)

54 MAXIMIAN (c.60; r.286-305; d.310) (W)

Diocletian Tetrarchy (293-305)

The withdrawal of forces from Gaul by Carinus had once more led to the collapse of the defences as well as the rise of the bagaudae (=bacaudae: peasant insurgents), who were led by the usurpers Amandus and Aelianus. The Alamanni and Burgundians had raided across the upper Rhine, and so had the Chaiboni and the western Heruli; the Franks and Saxons were ravaging the coasts of Gaul and the mouth of the Rhine; and the Sarmatians had invaded the Balkans.

Diocletian’s first priority was to re-establish order in the provinces and to restore the frontiers of the Empire, which had become too large for one man to govern effectively and Rome was no longer its strategic centre. Soon after the Battle of Margus he named a fellow soldier ²⁵Aurelius Valerius Maximianus (c.60; fl.285-310), as caesar, and later equated the earthly association of the two men with a partnership of the gods Jupiter and Hercules, himself taking the name Jovius and Maximianus that of Herculius. At this point, the Principate ended and gave way to the ‘Dominate Period’ (284-476), because under Diocletian and his successors the emperor was officially recognized as dominus (‘lord and master’).

In early 286 Maximian entered Gaul. He suppressed the insurrection by the bagaudae; cleared the left (east) bank of Rhine; drove the Heruli and Chaibones out of the country; and, basing himself at Mainz, conducted a successful defensive campaign against the Alamanni and Burgundians and for these successes he was rewarded with the rank of augustus. 

During the remainder of the year he fought the Franks on the coast of Gaul and around the lower Rhine. By 288 he had secured Gaul and the Rhine. At some point he received the submission of Franconian king Gennobaudes and all his people on the lower Rhine, and settled Friesians, Franks and Chamavi between the Waal and the Rhine, with obligations to defend their newly awarded lands from other tribes and to provide men for the Roman army.

While Maximian was fighting in Gaul and on the Rhine, Diocletian confronted the Sarmatians (eastern Europe) who having been driven southwards across the Danube by the Goths and other tribes, were demanding assistance in regaining their former territories or the right of pasturage inside the Empire. Diocletian refused their demands and made war on them, but although he won battles he was unable to eliminate the problem entirely (285). By 289 the Sarmatians had regrouped and from the war that ensued no details have survived but victory for the Romans was probably rapid.

In 286/7 Diocletian journeyed to Thracia and then into Syria. Narseh (r.293-302), a son of Shapur-I, had been placed in control of Armenia. Diocletian negotiated a peace with Bahram II in which Narseh was replaced in Armenia by the pro-Roman Tiridates III (c.80; r.287-330), Mesopotamia was re-absorbed into the Empire, and construction started on the Strata Diocletiana, a road with forts and garrisons situated at one day’s march, between Palmyra and Damascus.

Thus relieved of the necessity of mounting a campaign against Persia, Diocletian took his army to the West where he joined Maximian and embarked on a joint campaign against the Alamanni in 288. With Diocletian probably operating from Raetia while Maximian attacked from Moguntiacum (=Mainz), they cleared the agri decumates of the tribesmen who had overrun the area when the frontier fell in 264. 

In 290 Diocletian had to put down uprisings, probably instigated by the Persians, by the Saracens (Arab tribes) in the Syrian Desert and the Blemmyan nomads of southern Egypt.

In 293 Diocletian carried the delegation of the emperor’s functions a stage further. He nominated two young officers, ¹⁵Flavius Valerius Constantius (56; fl.283-306) and Gaius ⁰²Galerius Valerius Maximianus (51; fl.305-311) as caesares, i.e. heirs-elect of the two senior rulers.

Diocletian assigned responsibilities between himself and his colleagues on a territorial basis. As senior partner Diocletian took the East and Egypt, allotted most of the Balkans to his caesar, Galerius; and assigned Italy, Africa, Spain and the northern frontier to Maximian, whose caesar, Constantius, received Gaul and Britain. Each of the four rulers then set about restoring peace in his own part of the Empire.

In Persia the warlike Narseh (r.293-302) overthrew Bahram III (r.293), son of Bahram II, and Galerius, after crushing the revolt of Busiris and Coptos in Upper Egypt, was directed towards the frontier (Limes Arabicus) on the eastern border of Arabia Petraea. In 294 Diocletian defeated the Sarmatians and two years later campaigned against the Carpi on the lower Danube. In 296 Maximian with an army marched through Spain in the autumn. Crossing the Gibraltar Strait, he campaigned across North Africa against a rebel tribe called the Quinquegentiani, ending up triumphantly in Carthage in 298. In 297 ¹⁴Domitius Comitianus, backed by ²⁷Aurelius Achilleus, declared himself augustus at Alexandria. He was dead by December of that year, but Achilleus, with the title corrector, held out against an eight-month siege by Diocletian and finally fell in spring 298.