A son of Poseidon and Ceroëssa, the daughter of Zeus and Io. He was believed to be the founder of Byzantium. (Steph. Byz. s. v.; Diod. iv. 49.) This transplantation of the legend of Io to Byzantium suggests the idea, that colonists from Argos settled there. The leader of the Megarians, who founded Byzantium in n. c. 658, was likewise called Byzas. (Müller, Dor. i. 6. § 9.)