Queen Cassiopea of Aethiopia had bragged she was more beautiful than the Nereids (nymph-daughters of the sea-god Nereus). To punish her , Poseidon sent a sea monster Cetus that ravaged the coasts of Aethiopia. From the oracle of Delphi the king learned he had to sacrifice his daughter Andromeda. Andromeda was chained naked to a rock at the sea. Perseus on his way back, after having slain Medusa, found and freed her and killed Cetus. Here Perseus leads Andromeda down the rock.
