Perseus used Medusa’s head to rescue Andromeda from a sea monster in Greek mythology.
After killing Medusa, Perseus encountered Andromeda chained to a rock as a sacrifice to a sea monster. Her mother, Cassiopeia, had offended the sea gods by boasting about her beauty, and the kingdom was punished by the monster’s arrival. Perseus offered to save Andromeda and later used Medusa’s petrifying head against the creature.
The rescue is a separate episode within the larger Perseus cycle. It explains why Perseus and Andromeda became a famous heroic couple in classical mythology and why both figures appear as constellations in later astronomical tradition.
Different ancient and modern versions vary in the monster’s name and in the exact sequence of events. The stable central point is that Perseus used the magical power of Medusa’s severed head to defeat the threat and save Andromeda.