Sandro del Prete

With help from Pegasus and the head of the decapitated Medusa, Perseus liberates Andromeda from the monster Cetus. In the foreground (the lower image), queen Cassiopeia anxiously watches the fight. She is Andromeda's mother and partly to blame her daughter's tragic fate. Upon closer scrutiny, one begins to wonder whether Cassiopeia is really there, or whether this is not just another illusion.

The detail (above) of Cassiopeia's head revelas that of the decapitated Medusa, whose gaze transmogrified everything into stone.