Though deprived of a liberty which had for long years been almost nominal, Byzantium could not be deprived of its unrivalled position for commerce. It continued to flourish under the Pax Romana, the long-continued peace which all the inner countries of the empire enjoyed during the first two centuries of the imperial régime, and is mentioned again and again as one of the most important cities of the middle regions of the Roman world.
But an evil time for Byzantium, as for all the other parts of the civilized world, began when the golden age of the Antonines ceased, and the epoch of the military emperors followed. In 192 a.d., Commodus, the unworthy son of the great and good Marcus Aurelius, was murdered, and ere long three military usurpers were wrangling for his blood-stained diadem. Most unhappily for itself Byzantium lay on the line of division between the eastern provinces, where Pescennius Niger had been proclaimed, and the Illyrian provinces, where Severus had assumed the imperial style. The city was seized by the army of Syria, and strengthened in haste. Presently Severus appeared from the west, after he had made himself master of Rome and Italy, and fell upon the forces of his rival Pescennius. Victory followed the arms of the Illyrian legions, the east was subdued, and the Syrian emperor put to death. But when all his other adherents had yielded, the garrison of Byzantium refused to submit. For more than two years they maintained the impregnable city against the lieutenants of Severus, and it was not till a.d. 196 that they were forced to yield. The emperor appeared in person to punish the long-protracted resistance of the town; not only the garrison, but the civil magistrates of Byzantium were slain before his eyes. The massive walls “so firmly built with great square stones clamped together with bolts of iron, that the whole seemed but one block,” were laboriously cast down. The property of the citizens was confiscated, and the town itself deprived of all municipal privileges and handed over to be governed like a dependent village by its neighbours of Perinthus.
Caracalla, the son of Severus, gave back to the Byzantines the right to govern themselves, but the town had received a hard blow, and would have required a long spell of peace to recover its prosperity. Peace however it was not destined to see. All through the middle years of the third century it was vexed by the incursions of the Goths, who harried mercilessly the countries on the Black Sea whose commerce sustained its trade. Under Gallienus in a.d. 263 it was again seized by an usurping emperor, and shared the fate of his adherents. The soldiers of Gallienus sacked Byzantium from cellar to garret, and made such a slaughter of its inhabitants that it is said that the old Megarian race who had so long possessed it were absolutely exterminated. But the irresistible attraction of the site was too great to allow its ruins to remain desolate. Within ten years after its sack by the army of Gallienus, we find Byzantium again a populous town, and its inhabitants are specially praised by the historian Trebellius Pollio for the courage with which they repelled a Gothic raid in the reign of Claudius II.
The strong Illyrian emperors, who staved off from the Roman Empire the ruin which appeared about to overwhelm it in the third quarter of the third century, gave Byzantium time and peace to recover its ancient prosperity. It profited especially from the constant neighbourhood of the imperial court, after Diocletian fixed his residence at Nicomedia, only sixty miles away, on the Bithynian side of the Propontis. But the military importance of Byzantium was always interfering with its commercial greatness. After the abdication of Diocletian the empire was for twenty years vexed by constant partitions of territory between the colleagues whom he left behind him. Byzantium after a while found itself the border fortress of Licinius, the emperor who ruled in the Balkan Peninsula, while Maximinus Daza was governing the Asiatic provinces. While Licinius was absent in Italy, Maximinus treacherously attacked his rival's dominions without declaration of war, and took Byzantium by surprise. But the Illyrian emperor returned in haste, defeated his grasping neighbour not far from the walls of the city, and recovered his great frontier fortress after it had been only a few months out of his hands [a.d. 314]. The town must have suffered severely by changing masters twice in the same year; it does not, however, seem to have been sacked or burnt, as was so often the case with a captured city in those dismal days. But Licinius when he had recovered the place set to work to render it impregnable. Though it was not his capital he made it the chief fortress of his realm, which, since the defeat of Maximinus, embraced the whole eastern half of the Roman world.
It was accordingly at Byzantium that Licinius made his last desperate stand, when in a.d. 323 he found himself engaged in an unsuccessful war with his brother-in-law Constantine, the Emperor of the West. For many months the war stood still beneath the walls of the city; but Constantine persevered in the siege, raising great mounds which overlooked the walls, and sweeping away the defenders by a constant stream of missiles, launched from dozens of military engines which he had erected on these artificial heights. At last the city surrendered, and the cause of Licinius was lost. Constantine, the last of his rivals subdued, became the sole emperor of the Roman world, and stood a victor on the ramparts which were ever afterwards to bear his name.
II. The Foundation Of Constantinople. (A.D. 328-330.)
When the fall of Byzantium had wrecked the fortunes of Licinius, the Roman world was again united beneath the sceptre of a single master. For thirty-seven years, ever since Diocletian parcelled out the provinces with his colleagues, unity had been unknown, and emperors, whose number had sometimes risen to six and sometimes sunk to two, had administered their realms on different principles and with varying success.
Constantine, whose victory over his rivals had been secured by his talents as an administrator and a diplomatist no less than by his military skill, was one of those men whose hard practical ability has stamped upon the history of the world a much deeper impress than has been left by many conquerors and legislators of infinitely greater genius. He was a man of that self-contained, self-reliant, unsympathetic type of mind which we recognize in his great predecessor Augustus, or in Frederic the Great of Prussia.
Though the strain of old Roman blood in his veins must have been but small, Constantine was in many ways a typical Roman; the hard, cold, steady, unwearying energy, which in earlier centuries had won the empire of the world, was once more incarnate in him. But if Roman in character, he was anything but Roman in his sympathies. Born by the Danube, reared in the courts and camps of Asia and Gaul, he was absolutely free from any of that superstitious reverence for the ancient glories of the city on the Tiber which had inspired so many of his predecessors. Italy was to him but a secondary province amongst his wide realms. When he distributed his dominions among his heirs, it was Gaul that he gave as the noblest share to his eldest and best-loved son: Italy was to him a younger child's portion. There had been emperors before him who had neglected Rome: the barbarian Maximinus I. had dwelt by the Rhine and the Danube; the politic Diocletian had chosen Nicomedia as his favourite residence. But no one had yet dreamed of raising up a rival to the mistress of the world, and of turning Rome into a provincial town. If preceding emperors had dwelt far afield, it was to meet the exigencies of war on the frontiers or the government of distant provinces. It was reserved for Constantine to erect over against Rome a rival metropolis for the civilized world, an imperial city which was to be neither a mere camp nor a mere court, but the administrative and commercial centre of the Roman world.
For more than a hundred years Rome had been a most inconvenient residence for the emperors. The main problem which had been before them was the repelling of incessant barbarian inroads on the Balkan Peninsula; the troubles on the Rhine and the Euphrates, though real enough, had been but minor evils. Rome, placed half way down