There are many legends related to the foundation of Istanbul. The most popular one is about a group of colonizers from the city Megara in Greece under the leadership of Byzas. They sailed out to look for a new place to settle 685 BC.
As it was the custom of the time, before any such undertaking an oracle had to be consulted. The oracle in the Apollo temple in the famous town of Delphi advised Byzas to settle opposite the "land of the blind". The migrants searched for such a land for a long time. Eventually when they came to the headland of present-day Istanbul, they were delighted with what they found, a fertile land, a natural harbour and strait "Bosphorus" access to the open seas. To their surprise the presence of earlier settlers across the sea on the other side. The migrants decided that those people must have been blind if they could not appreciate the opportunities of this ideal place by settling on the opposite shore. So they were convinced that they had found the land the oracle had described.
In 343 BC Byzantium joined the Second Athenian League, throwing off the siege of Philip II of Macedon three years later. The lifting of the siege was attributed to the divine intervention of the goddess Hecate and was commemorated by the striking of coins bearing her star and crescent. Byzantium accepted Macedonian rule under Alexander the Great, regaining independence only with the eclipse of Macedonian might.
In 196 AD the city of Byzas made a fundamental mistake and sided with Pescennius Niger against the victorious Septimius Severus. The city was besieged and occupied by the Romans and made suffer extensive damage. The Rome was quick to realize the importance of this city so emperor Septimius Severus rebuilt and compensated the losses he inflicted upon the inhabitants. Before long it regained its previous prosperity, and temporarily renamed as Augusta Antonina by the emperor, in honor of his son. The hippodrome we see today is from emperor Septimius Severus time.
Later, in 330 AD it was officially declared by Constantine the Great as the capital of the Roman Empire. Many ceremonies were organized for the occasion, which marked the beginning of a golden age. Although the city was initially called the Second Rome or New Rome, these names were soon forgotten to be replaced by "Byzantium" and in later ages by "Constantinopolis".