The age of Constantine the Great can reasonably be seen as the watershed between the old Roman Empire and the new Byzantine Empire. Such a division is, to some degree, artificial, dependent on historians’ need to break the past up into comprehensible chunks: many elements of ancient civilization survived for centuries into the Byzantine period, and many historians regard Byzantium as, in fact, a survival of the ancient world. Indeed the Byzantines themselves recognized their connection to the Roman Empire and, for the whole of the Byzantine Empire (and even after its fall!) they continued to refer to themselves as “Romans.”
Nonetheless, it is clear that the early fourth century witnessed many new phenomena that were henceforth to characterize the Byzantine Empire, and what emerged from those changes was a society significantly different from what had come before. The most significant of these changes were the emergence of Christianity as the favored (and then the official) religion of the state and the creation of Constantinople as the new urban center of the empire on the shores of the Bosphoros, mid-way between all the empire’s frontiers.
The period was also marked by many other changes, some connected with these two overarching phenomena, others independent of them, and many with deep roots in the crises of the third century. These changes did not take place in a single moment and many of them took years, or even centuries, to work themselves out, one of the reasons that led historians to view the Byzantine period, or at least its early years, as one of transformation, as a bridge between the ancient and the medieval worlds, or even between the ancient and the modern worlds.
In AD 305 the arrangement of the imperial college was as follows:
Caesar Constantius Chlorus
On 1 May 305 Diocletian formally abdicated in the presence of his soldiers at Nikomedia, after a rule of over 20 years that put the Roman state on a new foundation. Diocletian pressured Maximian to abdicate at the same time, although it is clear that the latter was not really ready to do so. By the arrangements already agreed upon, Galerius and Constantius Chlorus became Augusti. These changes of course required the nomination of new Caesares. Both Constantius and Maximian had capable sons (Constantine and Maxentius, respectively), who were eager to participate in the imperial college.
Galerius, however, hated Maximian and his son, while Diocletian was always suspicious of Constantine, and he strongly opposed the nomination of sons to succeed their fathers, since this would introduce the principle of hereditary succession into the system. As a result, Maximinus Daia, Galerius’ nephew, became Caesar in the East, while Flavius Valerius Severus became Caesar in the West – and the old Augusti withdrew into retirement, Diocletian to his monumental palace at Split on the Dalmatian coast.
The official arrangement from 305 to 308, then, was as follows:
Caesar Maximinus Daia
Augustus Constantius Chlorus
Galerius clearly was the strong man in this system, in part because both Maximinus Daia and Severus were his appointees and neither was strong enough to act against him. Constantine, the son of Constantius, was a virtual hostage at Galerius’ court, in part to assure Constantius’ cooperation in the new arrangement.
As one of his first actions, Constantius Chlorus undertook a military expedition in Britain. In 306 the Picts, a people native to what is now Scotland, invaded Roman Britain and Constantius wished to push them back. He sought Galerius’ permission to have Constantine join him in his campaign and Galerius agreed, although he perhaps changed his mind and attempted to bring Constantine back.
Constantius and his son reached Britain, but Constantius unexpectedly died at York, on 25 July 306, throwing the new arrangement of the Tetrarchy into total confusion. Throughout Roman history, the military troops were normally loyal to the sons of their commanders, and the soldiers of Constantius were no exception. Immediately upon the death of the Augustus the troops proclaimed Constantine as emperor. Constantine wrote to Galerius, asking him to ratify the situation (i.e., to recognize Constantine as Augustus) and he then went to southern Gaul to await an answer from the senior emperor. Galerius agreed to a compromise: Constantine was to be recognized as Caesar, while Severus was to be Augustus. Constantine agreed, and for the time being the Diocletianic system remained intact.
In the meantime, however, in Rome the Praetorian Guard was discontented with its loss of power and prestige, along with the people of Rome, who were now being forced to pay taxes. They thus joined in proclaiming Maximian’s son Maxentius as Caesar. Maxentius asked his father to return from retirement, and Maximian did so, resuming the title of Augustus. Galerius ordered Severus to attack Maxentius, but his troops mutinied and he fled to Ravenna, where he was killed in 307.
All parties agreed that only the prestige of Diocletian could save the situation, and Galerius organized a meeting at Carnuntum in 308, attended by Diocletian and Maximian. Galerius secured the support of the senior ex-emperors to appoint his old colleague Licinius as Augustus. Licinius had distinguished himself as a commander in Galerius’ Persian campaign and was thus an experienced general. Constantine and Maximinus Daia were required to accept the rank of Caesars.
Caesar Maximinus Daia
The conference was therefore directed primarily against Maxentius and served to isolate him from the “legitimate” emperors. Maxentius, however, remained in effective control of Rome. Constantine, meanwhile, divorced his first wife (Minervina), the mother of his son Crispus, and married Fausta, the daughter of Maximian (and thus the sister of Maxentius).
In 310, however, Constantine abandoned his adherence to the Herculian dynasty when Maximian attempted a coup against him and was subsequently murdered. Constantine then announced that he was descended from Claudius Gothicus and thus a member of the ancient Roman imperial family of the Flavians. At the same time he apparently selected Sol Invictus (the Unconquered Sun) as his patron deity, thus breaking with the religious patronage of both the ruling “families” of the Tetrarchy, but reaching back to one of the gods favored by several of the military emperors of the third century. In addition, the sun-god was apparently popular in Gaul, Constantine’s current base of power. During this period Constantine sought to strengthen his support in this area, while perhaps laying plans for an eventual attempt to control the whole of the empire.
While near death in 311 Galerius proclaimed the end of the persecution of the Christians and toleration for all religions throughout the empire. After his death cooperation among members of the Tetrarchy completely fell apart: Maximinus Daia sought to seize the lands that had belonged to Galerius, but he was opposed by Licinius. In this situation Maximinus Daia sought an alliance with Maxentius, while Licinius and Constantine opposed them.