Diocletian, Sept. 17, 284—May 1, 305.
Carinus, † 285.
Maximian associated in the government, 286.
Carausius, 288—293.
Galerius and Chlorus created Cæsars, 292.
1. The reign of C. Valerius Diocletian, aged 39—60, proclaimed emperor after the murder of Numerianus, by the troops in Chalcedon, begins a new section in Roman history. To the period of military despotism succeeded the period of partitions. After Diocletian had defeated Carinus the yet remaining Cæsar, in Upper Mœsia, where he was assassinated, he made M. Valerius Maximianus Herculius, a rough warrior who had hitherto been his comrade in arms, the sharer of his throne. Herculius now contended with the Alemanni and Burgundians on the banks of the Rhine, while Diocletian himself made head against the Persians. Nevertheless, the two Augusti soon found themselves unable to withstand the barbarians, who were pressing forward on every side, more especially as Carausius had usurped and maintained the title of Cæsar in Britain. Each of them, therefore, created a Cæsar: Diocletian chose C. Galerius, and Maximianus Flavius Constantius Chlorus, both of whom had distinguished themselves as generals, at that time the only road to advancement. The whole empire was now divided between these four rulers; so that each had certain provinces to govern and defend; without detriment, however, to the unity of the whole, or to the dependence in which a Cæsar stood as the subordinate assistant and future successor of his Augustus.
In the partition, 292, Diocletian possessed the eastern provinces; Galerius, Thrace, and the countries on the Danube (Illyricum); Maximianus, Italy, Africa, and the islands; and Constantius, the western provinces of Gaul, Spain, Britain, and Mauritania.
2. This new system could not but have a striking effect upon the spirit of the government. It was now not only in fact, but also in form, entirely in the hands of the rulers. By their continual absence from Rome they became freed from that moral restraint in which the authority of the senate, and the name of the republic, not yet entirely laid aside, had held before them. Diocletian formally assumed the diadem, and, with the ornaments of the east, introduced its luxuries into his court. Thus was laid the foundation of that structure which Constantine the Great had to complete.
296.
3. The consequences of this new system became also oppressive to the provinces, inasmuch as they had now to maintain four rulers, with their courts, and as many armies. But however loud might be the complaints of the oppression occasioned thereby, it was, perhaps, the only means of deferring the final overthrow of the whole edifice. In fact, they succeeded not only in defeating the usurpers, Allectus in Britain 293—296. (who had murdered Carausius in 293), Julian in Africa, and Achilleus in Egypt; but also in defending the frontiers, which, indeed, by the victories of Galerius over the Persians, they extended as far as the Tigris. Did not, however, the gloomy perspective present itself, that among so many rulers, and the undefined relations which existed between the Cæsars and the emperors, the union could not be of long continuance?
Constantius, 305—307.
Galerius, 305—313.
4. Diocletian voluntarily abdicated the throne (although the growing power and encroaching disposition of Galerius might perhaps have had some influence), and obliged his colleague Maximianus to do the same. The two Cæsars, Constantius and Galerius, were proclaimed Augusti, and altered the division of the empire, so that the former possessed all the western countries, of which, however, he freely ceded Italy and Africa to Galerius, who had all the remaining provinces. The latter, during the same year, created Flavius Severus, Cæsar, and confided to him the government of Italy and Africa; as he did also C. Galerius Maximin, to whom he gave the Asiatic provinces. The administration of the two emperors, however, was very different; Constantius was as much beloved for his mild and disinterested government, as Galerius was hated for his harshness and prodigality. Constantius died very soon after at York, leaving his son Constantine heir to his dominions, who was immediately proclaimed Augustus by the legions, although Galerius would only acknowledge him as Cæsar.
Constantine the Great, July 25, 306—May 22, 337.
5. Thus Constantine, who afterwards obtained the surname of Great, began to rule, aged 33—64, though at first only over Britain, Spain, and Gaul; nevertheless, after seventeen years of violence and warfare, he succeeded in opening himself a way to the sole dominion of the empire. The rulers disagreed among themselves; and formidable usurpers started up and rendered war inevitable.