Part of the Thetis and Oceanus mosaic. Antakya, 2nd century AD. Mosaic of the Kalender with Oceanus and Thetis. Enc. Britt. About Thetis: From the Enc. Britt.: in Greek mythology, a Nereid loved by Zeus and Poseidon. When Themis (goddess of Justice), however, revealed that Thetis was destined to bear a son who would be mightier than his father, the two gods gave her to Peleus, king of the Myrmidons of Thessaly. Thetis, unwilling to wed a mortal, resisted Peleus' advances by changing herself into various shapes. But, assisted by the wise centaur Chiron, Peleus finally captured her.
All the gods brought gifts to their wedding. The child of their union was the warrior Achilles, but, according to some authorities, Thetis bore seven children, all of whom perished either when she attempted to render them immortal by fire or when she destroyed them as the tokens of an unwilling alliance. She befriended Zeus when the other gods revolted, and she rescued both Hephaestus and Dionysus from the sea. She had a sanctuary at Sparta.