Andromeda, daughter of Cepheus and Cassiopeia. Cassiopeia had boasted that she was more beautiful than the Nereids, and Poseidon offended had sent a sea monster to ravage the country. The monster could be diverted from utter destruction of the land only by Andromeda's being offered to him and accordingly, she was chained to a rock on th seashore. She was rescued however, by Perseus who passed by on his return from decapitating Medusa. He killed the monster and turn her uncle and others, who opposed his marrying the maiden in to stone by exposing the head of Medusa. Perseus, Andromeda, Cassipeia and even the monster were dignified by being turned into constellations. The sea monster is Cetus.