Semystra (Ancient Greek: Σημύστρα, romanized: Sēmústra) or Semestra was a nymph, in Greek mythology.
Semystra nurtured Keroessa, daughter of Io and Zeus.
Keroessa's mother gave birth at Semystra's altar and left the baby there in order to protect her from Hera.
[1][2] According to a legend, Semystra was also the mother of Byzas, who was the founder of Byzantium.
[1][2] This article relating to a Greek deity is a stub.