In ancient Greece, the head of MEDUSA represented protection against the profane. It was used to decorate city gates in the hope that it would offer protection against invaders.
The Goddess Athena placed the Medusa head on her shield the aegis and it supposedly turned anyone looking at it to stone.

Though the late classical legends of MEDUSA are rather gruesome, the Medusa head is essentially a symbol of protection, very similar to the terrifying carved faces that adorn the fagade of Balinese temples.