The first historically significant settlement here was founded by a Megarian colonist named Byzas from Greece. Before coming here, he consulted the oracle in Delphi to find a new settlement. The answer was ‘opposite the blind’. When Byzas and his small colony came to the Bosphorus in 657 BC, they saw a small colony living on the Asian shore at Chalcedon. They saw the superb natural harbour of the Golden Horn on the European shore and thought ‘those people in Chalcedon must be blind’. They called their new settlement ‘Byzantium’.
Over the next thousand years, Byzantium became a trade and commerce center.
In 324 AD, Constantine I defeated Licinius and became sole ruler of the Roman Empire. He also began to build a new capital at Byzantium, later named Constantinople (Constantine's polis or city). Byzantium submitted willingly to Roman Empire.
In 330 AD, Christianity was declared the official religion of the Roman Empire and Constantinople was dedicated as capital of the Byzantine Empire and splendidly rebuilt by Constantine I.
Constantinople itself was not only the new capital of the Empire but also the symbol of the Christendom. After the death of Constantine in 337, two of his sons, Constantius II and Constans took over the leadership of the empire. Constans, ruler of the western provinces, was, like his father, a Christian. In 341, he decreed that all pre-Christian Graeco Roman worship and sacrifice should cease; warning those who still persisted in practicing ancient Graeco-Roman polytheism with the threat of the death penalty.
Istanbul is famous as one of the most often besieged cities in the world. Before it was conquered by the Turks in 1453, its assailants included the Persian Darius (513 BC), the Athenian Alcibiades (408 BC), the Macedonian Philip II (339 BC), the Arabs (673-78, 717-18 AD), the Bulgarians (813, 913 AD) and the armies of the Fourth Crusade, which twice succeeded in taking the city (1203, 1204 AD). After Constantinople was taken by the Turks, the city became the capital of the Ottoman Empire until 1923, when the newly founded Turkish Republic declared Ankara (then Angora) the capital. From 1918 until 1923 Great Britain, France and Italy occupied the city.
Under the Ottomans, the city went through several name changes, among them Konstantiniyye, Polis, Stimpol, Estanbul, Istambol and Istanbul. The name was officially changed to Istanbul in 1930.