There are many fairytales present about the foundation of Istanbul. According to the most spreaded fairytale the beloved of Zeus, Io, has turned into a cow by Hera, out of jealousy. Hera is the sister and wife of Zeus and the goddess of marriage. Later, Hera, while flewing from a God who didn’t leave her alone, gave birth to her daughter Kerroessa. This girl has been raised by the nimph Semestra. After the girl has been raised she married Poseidon, the God of the sea and gave birth to a boy called Byzas. This Byzas is the Byzas who founded Istanbul.
Another fairytale is that emigrants from Karia came from Megara to the Bosphorus to start a new life and established Khalkedon (Kadikoy) in 680 before Christ. Hereby, according to findings from digging up in Fikirtepe in the North of Kadikoy, one assumes that there is/has been an earlier establishment.
From Persian King Darius to Alexander the Great
Darius the Great has conquerred Byzantium as well as Khalkedon during the Iskit Seferi on his way to Trakya. In 409 before Christ, the city was conquerred by the Athen commander Alkibiades and in 405 conquerred by the Spartans. The Macedonian King Philip II has surrounded Byzantium from land and from sea in 340 before Christ, but has never been able to conquer it.
Alexander the Great has made victories till the lands of India in 333 before Christ, but has not been able to conquer Byzantium. In 657 before Christ, Istanbul is established first in Sarayburnu by Byzas (coming from Megara). Because the first name of the city was Byzas the city was called Byzantium till the 2nd century after Christ. The reason for this name was because –ion was added to Byzas (in Latin byzas-byzantion).