Medusa was one of the three Gorgons in Greek mythology. She had living snakes instead of hair, and anyone who looked at her turned to stone. Her sisters were Stheno and Euryale, and their parents were Phorcys and Ceto. Medusa was the only one of the three who was mortal. The hero Perseus cut off her head and used it as a weapon, because it could still turn people to stone, and later he gave it to Athena to put on her shield. The ancient Greeks used the image of her head, called the Gorgoneion, to keep evil away.