In Greek mythology Medusa ( ), "guardian, protectress") was a Gorgon, a chthonic monster, and a daughter of Phorcys and Ceto; Only Hyginus, (Fabulae, 151) interposes a generation and gives another chthonic pair as parents of Medusa; until he gave it to the goddess Athena to place on her shield. In classical antiquity the image of the head of Medusa appeared in the evil-averting device known as the Gorgoneion.
The three Gorgon sisters—Medusa, Stheno, and Euryale—were children of the ancient marine deities Phorcys (or Phorkys) and his sister Ceto (or Keto), chthonic monsters from an archaic world. Their genealogy is shared with other sisters, the Graeae, as in Aeschylus's Prometheus Bound who places both trinities of sisters far off "on Kisthene's dreadful plain":
Near them their sisters three, the Gorgons, winged
With snakes for hair— hated of mortal man—
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