A Dalmatian soldier named Diocles had been told by a witch that he should become Emperor by the slaughter of a boar. He became a great hunter, but no wild boar that he killed seemed to bring him nearer to the purple, till, when the army was fighting on the Tigris, the Emperor Numerianus died, and an officer named Aper offered himself as his successor. Aper is the Latin for a boar, and Diocles, perceiving the scope of the prophecy, thrust his sword into his rival's breast, and was hailed Emperor by the legions. He lengthened his name out to Diocletianus, to sound more imperial, and began a dominion unlike that of any who had gone before. They had only been, as it were, overgrown generals, chosen by the Prætorians or some part of the army, and at the same time taking the tribuneship and other offices for life. Diocletian, though called Emperor, reigned like the kings of the East. He broke the strength of the Prætorians, so that they could never again kill one Emperor and elect another as before; and he never would visit Rome lest he should be obliged to acknowledge the authority of the Senate, whose power he contrived so entirely to take away, that thenceforward Senator became only a complimentary title, of which people in the subdued countries were very proud.
He divided the empire into two parts, feeling that it was beyond the management of any one man, and chose an able soldier of low birth but much courage, named Maximian, to rule the West from Trier as his capital, while he himself ruled the East from Nicomedia. Each of the two Emperors chose a future successor, who was to rule in part of his dominions under the title of Cæsar, and to reign after him. Diocletian chose his son-in-law Galerius, and sent him to fight on the Danube; and Maximian chose, as Cæsar, Constantius Chlorus, who commanded in Britain, Gaul, and Spain; and thus everything was done to secure that a strong hand should be ready everywhere to keep the legions from setting up Emperors at their own will.
Diocletian was esteemed the most just and kind of the Emperors; Maximian, the fiercest and most savage. He had a bitter hatred of the Christian name, which was shared by Galerius; but, on the other hand, the wife of Diocletian was believed to be a Christian, and Helena, the wife of Constantius, was certainly one. However, Maximian and Galerius were determined to put down the faith. Maximian is said to have had a whole legion of Christians in his army, called the Theban, from the Egyptian Thebes. These he commanded to sacrifice, and on their refusal had them decimated—that is, every tenth man was slain. They were called on again to sacrifice, but still were staunch, and after a last summons were, every man of them, slain as they stood with their tribune Maurice, whose name is still held in high honor in the Engadine. Diocletian was slow to become a persecutor, until a fire broke out in his palace at Nicomedia, which did much mischief in the city, but spared the chief Christian church. The enemies of the Christians accused them of having caused it, and Diocletian required every one in his household to clear themselves by offering sacrifice to Jupiter. His wife and daughter yielded, but most of his officers and slaves held out, and died in cruel torments. One slave was scourged till the flesh parted from his bones, and then the wounds were rubbed with salt and vinegar; others were racked till their bones were out of joint, and others hung up by their hands to hooks, with weights fastened to their feet. A city in Phrygia was surrounded by soldiers and every person in it slaughtered; and the Christians were hunted down like wild beasts from one end of the empire to the other, everywhere save in Britain, where, under Constantius, only one martyrdom is reported to have taken place, namely, that of the soldier at Verulam, St. Alban. It was the worst of all the persecutions, and lasted the longest.
The two Emperors were good soldiers, and kept the enemies back, so that Diocletian celebrated a triumph at Nicomedia; but he had an illness just after, and, as he was fifty-nine years old, he decided that it would be better to resign the empire while he was still in his full strength, and he persuaded Maximian to do the same, in 305, making Constantius and Galerius Emperors in their stead. Constantius stopped the persecution in the West, but it raged as much as ever in the East under Galerius and the Cæsar he had appointed, whose name was Daza, but who called himself Maximin. Constantius fought bravely, both in Britain and Gaul, with the enemies who tried to break into the empire. The Franks, one of the Teuton nations, were constantly breaking in on the eastern frontier of Gaul, and the Caledonians on the northern border of the settlement of Britain. He opposed them gallantly, and was much loved, but he died at York, 305, and Galerius passed over his son Constantine, and appointed a favorite of his own named Licinius. Constantine was so much beloved by the army and people of Gaul that they proclaimed him Emperor, and he held the province of Britain and Gaul securely against all enemies.
Old Maximian, who had only retired on the command of Diocletian, now came out from his retreat, and called on his colleague to do the same; but Diocletian was far too happy on his little farm at Salona to leave it, and answered the messenger who urged him again to take upon him the purple with—"Come and look at the cabbages I have planted." However, Maximian was accepted as the true Emperor by the Senate, and made his son Maxentius, Cæsar, while he allied himself with Constantine, to whom he gave his daughter Fausta in marriage. Maxentius turned out a rebel, and drove the old man away to Marseilles, where Constantine gave him a home on condition of his not interfering with government; but he could not rest, and raised the troops in the south against his son-in-law. Constantine's army marched eagerly against him and made him prisoner, but even then he was pardoned; yet he still plotted, and tried to persuade his daughter Fausta to murder her husband. Upon this Constantine was obliged to have him put to death.
Galerius died soon after of a horrible disease, during which he was filled with remorse for his cruelties to the Christians, sent to entreat their prayers, and stopped the persecution. On his death, Licinius seized part of his dominions, and there were four men calling themselves Emperors—Licinius in Asia, Daza Maximin in Egypt, Maxentius at Rome, and Constantine in Gaul.
There was sure soon to be a terrible struggle. It began between Maxentius and Constantine. This last marched out of Gaul and entered Italy. He had hitherto seemed doubtful between Christianity and paganism, but a wonder was seen in the heavens before his whole army, namely, a bright cross of light in the noon-tide sky with the words plainly to be traced round it, In hoc signo vinces—"In this sign thou shalt conquer." This sight decided his mind; he proclaimed himself a Christian, and from Milan issued forth an edict promising the Christians his favor and protection. Great victories were gained by him at Turin, Verona, and on the banks of the Tiber, where, at the battle of the Milvian Bridge in 312, Maxentius was defeated, and was drowned in crossing the river. Constantine entered Rome, and was owned by the Senate as Emperor of the West.