(Θέτις), one of the daughters of Nereus and Doris, was the wife of Peleus, by whom she became the mother of Achilles. (Hom. Il. 1.538, 18.35, &c., 52, &c.; Hes. Theog. 244.) Later writers describe her as a daughter of Cheiron (Schol. ad Apollon. Rhod. 1.558). According to others, Peleus married Philomela, the daughter of Actor, but his friend Cheiron, wishing to render Peleus celebrated, spread the report that he was married to Thetis. (Schol. ad Apollon. Rhod. 4.816.) Being a granddaughter of Poseidon, Catullus (64. 28) calls her Neptunine. As a marine divinity, she dwelt like her sisters, the Nereids, in the depth of the sea, with her father Nereus. (Hom. Il. 1.358, 18.36, 20.207.) She there received Dionysus on his flight from Lycurgus, and the god, in his gratitude, presented her with a golden urn. (Hom. Il. 6.135, Od. 24.75; comp. Tzetz. ad Lycoph. 273.) When Hephaestus was thrown down from heaven, he was likewise received by Thetis. She had been brought up by Hera (Il. 24.60), and when she reached the age of maturity, Zeus and Hera gave her, against her own will, in marriage to Peleus. Poseidon and Zeus himself are said by some to have sued for her hand (Pind. Isthm. 8.58), but when Themis declared that the son of Thetis would be more illustrious than his father, both suitors desisted. (Pind. l.c. 8.70; Ov. Met. 11.225, 15.856, 11.350, &c.; Aeschyl. Prom. 767 ; Hygin. Fab. 54 ; Serv. ad Virg. Eclog. 6.42.) Others state that Thetis rejected the offers of Zeus, because she had been brought up by Hera (Hom. Il. 24.60; Apollon. 4.793); and the god, to revenge himself, decreed that she should marry a mortal. Cheiron then informed his friend Peleus how he might gain possession of her, even if she should metamorphose herself; for Thetis, like Proteus, had the power of assuming any form she pleased, and she had recourse to this means of escaping from Peleus, but the latter did not let her go, until she again assumed her proper form. (Apollod. 3.13.5; Pind. N. 3.60; Paus. 8.18. § l.) Others again relate, that a marine divinity appeared to Peleus on Mount Pelion, and testified her love to him, but without revealing herself to him. Peleus, however, who saw her playing with dolphins, recognised the goddess, and henceforth shunned her presence. But she encouraged him, reminding him of the love of Eos to Tithonus, of Aphrodite to Anchises, &c., and promised to present him with a son who should be more illustrious than any mortal. (Philostr. Her. 19. 1.) The wedding of Pelens was honoured with the presence of all the gods. (Hom. Il. 24.62.) After she had become the mother of Achilles, she bestowed upon him the tenderest care and love. (Hom. Il. 1.359, 500, &c., 8.370, 18.73, 457; comp. ACHILLES.) Her prayers to Zeus for him were listened to, because at one time, when Zeus was threatened by the other gods, she induced Briareus or Aegaeon to come to his assistance. (Hom. Il. 1.396, &c.) Thetis had a temple (Thetideion) between Old and New Pharsalus in Thessaly (Strab. ix. p.431), and in Sparta and Messenia she was likewise worshipped. (Paus. 3.14.4, 22.2.)