The little colony founded by Byzas, the Megarian, had prospered marvellously, though it had experienced to the full all the vicissitudes of fortune. It had fallen before the Persian King Darius; it had been wrested from him after a long siege by Pausanias, the hero of Platæa, when the Greeks rolled back the tide of invasion. In turn the subject and successful rival of Athens, Byzantium gained new glory by withstanding for two years the assaults of Philip of Macedon. Thanks to the eloquence of Demosthenes, Athens sent help in the shape of ships and men, and, in commemoration of a night attack of the Macedonians successfully foiled by the opportune rising of the moon, Byzantium placed upon her coins the crescent and the star, which for four centuries and a half have been the familiar symbols of Turkish sovereignty. Byzantium grew rich on commerce. It was the port of call at which every ship entering or leaving the Bosphorus was bound to touch; no craft sailed the Euxine without paying dues to the city at its mouth. Polybius, in a very interesting passage,[120] points out how Byzantium occupied “the most secure and advantageous position of any city in our quarter of the world, as far as the sea is concerned.” Then he continues: “The Pontus, therefore, being rich in what the rest of the world requires to support life, the Byzantines are absolute masters in this respect. For the first necessaries of existence, cattle and slaves, are admittedly supplied by the region of the Pontus in better quality and greater profusion than elsewhere. In the matter of luxuries, they supply us with honey, wax, and salt fish, while they take our superfluous olive oil and wines.” ----- Footnote 120: Bk. IV., c. 38, _seq._ ----- It was Byzantium, therefore, which kept open the straits, and Polybius speaks of the city as a common benefactor of the Greeks. When the Romans began to appear on the scene as a world-power, Byzantium made terms with the Senate. It well suited the Roman policy to have a powerful ally on the Bosphorus, strong in the ships in which Rome was usually deficient. As a _libera et fœderata civitas_, Byzantium enjoyed a more or less prosperous history until the days of Vespasian, who stripped it of its privileges. These were restored, but a shattering blow overtook the city at the close of the second century, when Septimus Severus took it by storm. Angry at its long resistance, Severus levelled its fortifications to the ground,—a work of endless toil, for the stones and blocks had been so clamped together that the walls were one solid mass. However, before he died, he repented him of the destruction which he had wrought and gave orders for the walls to be built anew. It was the Byzantium as rebuilt by Severus that Constantine determined to refound on a far more splendid scale. [Illustration: BAPTISTERY OF SAN GIOVANNI IN LATERAN, ROME. PHOTOGRAPH BY ALINARI. ]