InGreek mythology,Ceroessa (Ancient Greek: ΚερόεσσαKeroessa means "the horned") was a heroine of the foundational myth ofByzantium. She was the daughter ofIo andZeus; elder sister ofEpaphus; and mother ofByzas, founder of Byzantium, with her uncle,Poseidon.[1][2]
According to the historianHesychius of Miletus,[3] as Io, changed into a heifer and being chased by a gadfly on behalf of the jealousHera, was passing throughThrace, she gave birth to a girl, Keroessa, on the banks of theGolden Horn, by the altar of thenymphSemystra. According to legend, Keroessa's birthplace is called Semystra (today EyüpSultan district), where the rivers Kydaros (today Alibey Stream) and Barbyses (today Kağıthane Stream) flow into the sea at the end of Chrysokeras (Golden Horn or Haliç). Semystra takes its name from the Semystra Altar, where today Eyyub El Ensari's tomb is located, and its water is believed to have healing powers[4][5] but according to Swiss scholar Ernest Mamboury's notebook he thinks “Altar of Semystra" was Alibeyköy, Silahtaraga neighborhood in EyüpSultan district.[6] Keroessa was reared by Semystra and grew up surpassing other local maidens in beauty. She had intercourse with Poseidon and in due course gave birth to a son, whom she namedByzas. He became the founder of Byzantium (today Sarayburnu, where Topkapı Palace was built) and named the Golden Horn (Greek Χρυσόκερας) after his mother. Ceroessa also had another son namedStrombos. Strombos fought with his brother and the Byzantines.[7]
According toNonnus, Keroessa's birthplace was the same as that of her brother Epaphus, i. e. Egypt.[8]