The Megarians came into Istanbul from Greece through the Sea of Marmara in 680 BC. They established a colony on the acropolis above the Golden Horn oposite the Greek Colony of Chalcedon, which had been establiseh a few years earlier. The Chalcedon Colony was involved in architecture and referred to as "the Land of the Blind", possibly because they must have been blindnot to see the advantages of setting on the European side of the Bosphorus, which would be much more secure militarily. The Megarians, under the leadership of Byzas, acted according to a Delphic oracle in choosing the site. They were settled in today’s arayburnu nd the town became to be called Byzantium. It is thought that various Thracian poeple were living in the area and intermingled with Megarians. Byzantium, through becoming a commercial center and as a result of its being easily defensible, became a powerful, fast growing member of the Greek colonies.

In 513 BC. Byzantine was taken by the Persian leader Darius who had captured Anatolia. The city remained in Persian hands until it was taken by the Spartan general Pausanius in 477 BC. He in turn, set himself up as a tyrant and was driven out by the Athenians and surrendered to the Spartan commander Lysander in 403 after the final defeat of Athens in the Peloponnesian wars.

The city entered an uneasy allience with King Phiip of Macedonia (father of Alexander the Great) during which the city walls were repaired but surrendered without a battle to Alexander the Great in 344 BC. After his death in 323, the city was under the leadership of one of the generals of Alexander the Great, Antigonos, but more or less governed itself.

The city was overcome by hordes of Saxons arriving from the West in 278 BC. and was looted and forced to pay tributes. It was later captured by the allied forces of Rhodes, Pergamum and Bythinia under whose sovereignty the city remained until it was bequeathed to the Roman Empire by the last ruler of Pergamum.

The Macedonia - Roman wars ended in the sovereignty of Rome over the Balkans, Asia minor and Byzantium in 146 BC. and a period of peace ruled for the next 300 years.