In Greek mythology, Byzas (Greek: Βύζας) was the eponymous founder of Byzantium (Greek: Βυζάντιον), the city later known as Constantinople and Istanbul.
The tradition tells that Byzas, son of King Nisos (Νίσος), planned to found a Greek colony of the Dorian city of Megara. Byzas consulted the oracle of Apollo at Delphi, which instructed Byzas to settle opposite the "Land of the Blind". Leading a group of Megarian colonists, Byzas found a location where the Golden Horn, a great natural harbour, meets the Bosphorus and flows into the Sea of Marmara, opposite Chalcedon (modern day Kadıköy). He adjudged the Chalcedonians blind not to have recognized the advantages the land on the European side of the Bosphorus had over the Asiatic side. The European side (at Seraglio Point) featured only two fishing settlements: Lygos and Semistra. In 667 BCE he founded Byzantium at their location, thus fulfilling the oracle's requirement.
Son of Poseidon
According to Greek mythology, Byzas was a son of Poseidon by Keroessa. Zeus fell in love with Io, the daughter of Inachus, King of Argos and god of the river of Argos. Zeus temporarily transformed his mistress into a heifer in order to protect her from the wrath of his wife Hera. In her wanderings, Io crossed the Bosphorus, giving the strait its name ( βοός πόρος - boos poros, which is Greek for cow-ford). After reassuming her original form, she gave birth to a girl, Keroessa.
Keroessa later bore a son to Poseidon, elder brother of Zeus and lord of all waters from the Pillars of Hercules to the Hellespont. This son, Byzas the Megarian, in time became the founder of Byzantium and named the Golden Horn (Greek Χρυσοκέρας (Khrysokeras or Chrysoceras)) after his mother. Some sources say that Byzas was brought up by the naiad Byzia and married Phidaleia, daughter of King Barbyzos.
