How many Gorgon sisters were there?

The story behind the answer

There were three Gorgon sisters: Stheno, Euryale, and Medusa. In Greek myth, they were daughters of the sea deities Phorcys and Ceto, known for their snake hair and a gaze that turned onlookers to stone. Of the three, only Medusa was mortal—making her the target of the hero Perseus, who beheaded her with Athena’s help.

To remember: think “SEM” (Stheno–Euryale–Medusa), a three-letter cue for the three sisters. Medusa became the most famous because her severed head retained its petrifying power; Athena placed it on her aegis as a protective emblem. The trio symbolize primal terror at the edge of the world in Greek imagination.