Diocletian, peaceful in his Dalmatian palace, saw the failure of both the persecution and the tetrarchy. Seldom had the Empire witnessed such confusion as followed his abdication. Galerius prevailed upon Constantius to let him appoint Severus and Maximinus Daza as “Caesars” (305). At once the principle of heredity asserted its claims: Maxentius, son of Maximian, wished to succeed his father’s authority, and a like resolution fired Constantine.
Flavius Valerius Constantinus had begun life at Naissus in Moesia (272?) as the illegitimate son of Constantius by his legal concubine Helena, a barmaid from Bithynia.27 On becoming a “Caesar,” Constantius was required by Diocletian to put away Helena and to take Maximian’s stepdaughter Theodora as his wife. Constantine received only a meager education. He took up soldiering early, and proved his valor in the wars against Egypt and Persia. Galerius, on succeeding Diocletian, kept the young officer near him as a hostage for the good behavior of Constantius. When the latter asked Galerius to send the youth to him Galerius procrastinated craftily; but Constantine escaped from his watchers, and rode night and day across Europe to join his father at Boulogne and share in a British campaign. The Gallic army, deeply loyal to the humane Constantius, came to love his handsome, brave, and energetic son; and when the father died at York (306), the troops acclaimed Constantine not merely as “Caesar” but as Augustus—emperor. He accepted the lesser title, excusing himself on the ground that his life would be unsafe without an army at his back. Galerius, too distant to intervene, reluctantly recognized him as a “Caesar.” Constantine fought successfully against the invading Franks, and fed the beasts of the Gallic amphitheaters with barbarian kings.
Meanwhile in Rome the Praetorian Guard, eager to restore the ancient capital to leadership, hailed Maxentius as emperor (306). Severus descended from Milan to attack him; Maximian, to confound the confusion, returned to the purple at his son’s request, and joined in the campaign; Severus was deserted by his troops and put to death (307). To help himself face the growing chaos, the aging Galerius appointed a new Augustus—Flavius Licinius; hearing which, Constantine assumed a like dignity (307). A year later Maximinus Daza adopted the same title, so that in place of the two Augusti of Diocletian’s plan there were now six; no one cared to be merely “Caesar.” Maxentius quarreled with his father; Maximian went to Gaul to seek Constantine’s aid; while the latter fought Germans on the Rhine, Maximian tried to replace him as commander of the Gallic armies; Constantine marched across Gaul, besieged the usurper in Marseilles, captured him, and granted him the courtesy of suicide (310).
The death of Galerius (311) removed the last barrier between intrigue and war. Maximinus plotted with Maxentius to overthrow Licinius and Constantine, who conspired to overthrow them. Taking the initiative, Constantine crossed the Alps, defeated an army near Turin, and advanced upon Rome with a celerity of movement, and a restraining discipline of his troops, that recalled the march of Caesar from the Rubicon. On October 27, 312, he met the forces of Maxentius at Saxa Rubra (Red Rocks) nine miles north of Rome; and by superior strategy compelled Maxentius to fight with his back to the Tiber, and no retreat possible except over the Mulvian Bridge. On the afternoon before the battle, says Eusebius,28 Constantine saw a flaming cross in the sky, with the Greek words en toutoi nika—“in this sign conquer.”II Early the next morning, according to Eusebius and Lactantius,31 Constantine dreamed that a voice commanded him to have his soldiers mark upon their shields the letter X with a line drawn through it and curled around the top—the symbol of Christ. On arising he obeyed, and then advanced into the forefront of battle behind a standard (known henceforth as the labarum) carrying the initials of Christ interwoven with a cross. As Maxentius displayed the Mithraic-Aurelian banner of the Unconquerable Sun, Constantine cast in his lot with the Christians, who were numerous in his army, and made the engagement a turning point in the history of religion. To the worshipers of Mithras in Constantine’s forces the cross could give no offense, for they had long fought under a standard bearing a Mithraic cross of light.32 In any case Constantine won the battle of the Mulvian Bridge, and Maxentius perished in the Tiber with thousands of his troops. The victor entered Rome the welcomed and undisputed master of the West.
Early in 313 Constantine and Licinius met at Milan to co-ordinate their rule. To consolidate Christian support in all provinces, Constantine and Licinius issued an “Edict of Milan,” confirming the religious toleration proclaimed by Galerius, extending it to all religions, and ordering the restoration of Christian properties seized during the recent persecutions. After this historic declaration, which in effect conceded the defeat of paganism, Constantine returned to the defense of Gaul, and Licinius moved eastward to overwhelm Maximinus (313). The death of Maximinus shortly afterward left Constantine and Licinius the unchallenged rulers of the Empire. Licinius married Constantine’s sister, and a war-weary people rejoiced at the prospect of peace.
But neither of the Augusti had quite abandoned the hope of undivided supremacy. In 314 their mounting enmity reached the point of war. Constantine invaded Pannonia, defeated Licinius, and exacted the surrender of all Roman Europe except Thrace. Licinius revenged himself upon Constantine’s Christian supporters by renewing the persecution in Asia and Egypt. He excluded Christians from his palace at Nicomedia, required every soldier to adore the pagan gods, forbade the simultaneous attendance of both sexes at Christian worship, and at last prohibited all Christian services within city walls. Disobedient Christians lost their positions, their citizenship, their property, their liberty, or their lives.
Constantine watched for an opportunity not only to succor the Christians of the East, but to add the East to his realm. When barbarians invaded Thrace, and Licinius failed to move against them, Constantine led his army from Thessalonica to the rescue of Licinius’ province. After the barbarians were driven back Licinius protested Constantine’s entry into Thrace; and as neither ruler desired peace, war was renewed. The defender of Christianity, with 130,000 men, met the defender of paganism, with 160,000 men, first at Adrianople and then at Chrysopolis (Scutari), won, and became sole emperor (323). Licinius surrendered on a promise of pardon; but in the following year he was executed on the charge that he had resumed his intrigues. Constantine recalled the Christian exiles, and restored to all “confessors” their lost privileges and property. While still proclaiming liberty of worship for all, he now definitely declared himself a Christian, and invited his subjects to join him in embracing the new faith.