Byzantium, an ancient Greek city on the shores of the Bosporus, occupying the most easterly of the seven hills on which modern Constantinople stands. It was said to have been founded by Megarians and Argives under Byzas about 657 B.C., but the original settlement having been destroyed in the reign of Darius Hystaspes by the satrap Otanes, it was recolonized by the Spartan Pausanias, who wrested it from the Medes after the battle of Plataea (479 B.C.) - a circumstance which led several ancient chroniclers to ascribe its foundation to him. Its situation, said to have been fixed by the Delphic oracle, was remarkable for beauty and security. It had complete control over the Euxine grain-trade; the absence of tides and the depth of its harbour rendered its quays accessible to vessels of large burden; while the tunny and other fisheries were so lucrative that the curved inlet near which it stood became known as the Golden Horn. The greatest hindrance to its prosperity was the miscellaneous character of the population, partly Lacedaemonian and partly Athenian, who flocked to it under Pausanias. It was thus a subject of dispute between these states, and was alternately in the possession of each, till it fell into the hands of the Macedonians. From the same cause arose the violent intestine contests which ended in the establishment of a rude and turbulent democracy.
About seven years after its second colonization, the Athenian Cimon wrested it from the Lacedaemonians; but in 440 B.C. it returned to its former allegiance. Alcibiades, after a severe blockade (408 B.C.), gained possession of the city through the treachery of the Athenian party; in 405 B.C. it was retaken by Lysander and placed under a Spartan harmost. It was under the Lacedaemonian power when the Ten Thousand, exasperated by the conduct of the governor, made themselves masters of the city, and would have pillaged it had they not been dissuaded by the eloquence of Xenophon. In 390 B.C. Thrasybulus, with the assistance of Heracleides and Archebius, expelled the Lacedaemonian oligarchy, and restored democracy and the Athenian influence.
After having withstood an attempt under Epaminondas to restore it to the Lacedaemonians, Byzantium joined with Rhodes, Chios, Cos, and Mausolus, King of Caria, in throwing off the yoke of Athens, but soon after sought Athenian assistance when Philip of Macedon, having overrun Thrace, advanced against it. The Athenians under Chares suffered a severe defeat from Amyntas, the Macedonian admiral, but in the following year gained a decisive victory under Phocion and compelled Philip to raise the siege. The deliverance of the besieged from a surprise, by means of a flash of light which revealed the advancing masses of the Macedonian army, has rendered this siege memorable. As a memorial of the miraculous interference, the Byzantines erected an altar to Torch-bearing Hecate, and stamped a crescent on their coins, a device which is retained by the Turks to this day. They also granted the Athenians extraordinary privileges, and erected a monument in honour of the event in a public part of the city.
During the reign of Alexander Byzantium was compelled to acknowledge the Macedonian supremacy; after the decay of the Macedonian power it regained its independence, but suffered from the repeated incursions of the Scythians. The losses which they sustained by land roused the Byzantines to indemnify themselves on the vessels which still crowded the harbour, and the merchantmen which cleared the straits; but this had the effect of provoking a war with the neighbouring naval powers. The exchequer being drained by the payment of 10,000 pieces of gold to buy off the Gauls who had invaded their territories about 279 B.C., and by the imposition of an annual tribute which was ultimately raised to 80 talents, they were compelled to exact a toll on all the ships which passed the Bosporus - a measure which the Rhodians resented and avenged by a war, wherein the Byzantines were defeated. After the retreat of the Gauls Byzantium rendered considerable services to Rome in the contests with Philip II., Antiochus and Mithradates.
During the first years of its alliance with Rome it held the rank of a free confederate city; but, having sought arbitration on some of its domestic disputes, it was subjected to the imperial jurisdiction, and gradually stripped of its privileges, until reduced to the status of an ordinary Roman colony. In recollection of its former services, the emperor Claudius remitted the heavy tribute which had been imposed on it; but the last remnant of its independence was taken away by Vespasian, who, in answer to a remonstrance from Apollonius of Tyana, taunted the inhabitants with having "forgotten to be free." During the civil wars it espoused the party of Pescennius Niger; and though skilfully defended by the engineer Periscus, it was besieged and taken (A.D. 196) by Severus, who destroyed the city, demolished the famous wall, which was built of massive stones so closely riveted together as to appear one block, put the principal inhabitants to the sword and subjected the remainder to the Perinthians. This overthrow of Byzantium was a great loss to the empire, since it might have served as a protection against the Goths, who afterwards sailed past it into the Mediterranean. Severus afterwards relented, and, rebuilding a large portion of the town, gave it the name of Augusta Antonina. He ornamented the city with baths, and surrounded the hippodrome with porticos; but it was not till the time of Caracalla that it was restored to its former political privileges.
It had scarcely begun to recover its former position when, through the capricious resentment of Gallienus, the inhabitants were once more put to the sword and the town was pillaged. From this disaster the inhabitants recovered so far as to be able to give an effectual check to an invasion of the Goths in the reign of Claudius II., and the fortifications were greatly strengthened during the civil wars which followed the abdication of Diocletian. Licinius, after his defeat before Adrianople, retired to Byzantium, where he was besieged by Constantine, and compelled to surrender (A.D. 323-324). To check the inroads of the barbarians on the north of the Black Sea, Diocletian had resolved to transfer his capital to Nicomedia; but Constantine, struck with the advantages which the situation of Byzantium presented, resolved to build a new city there on the site of the old and transfer the seat of government to it. The new capital was inaugurated with special ceremonies, A.D. 330. (See Constantinople.)