Overview
In Greek mythology, Tethys was a Titan daughter of Uranus and Gaia, a sister and wife of the Titan Oceanus, and the mother of the river gods and the Oceanids. Although Tethys had no active role in Greek mythology and no established cults, she was depicted in mosaics decorating baths, pools, and triclinia in the Greek East, particularly in Antioch and its suburbs, either alone or with Oceanus.
Genealogy
Tethys was one of the Titan offspring of Uranus (Sky) and Gaia (Earth). Hesiod lists her Titan siblings as Oceanus, Coeus, Crius, Hyperion, Iapetus, Theia, Rhea, Themis, Mnemosyne, Phoebe, and Cronus. Tethys married her brother Oceanus, an enormous river encircling the world, and was by him the mother of numerous sons (the river gods) and numerous daughters (the Oceanids).
According to Hesiod, there were three thousand (i.e. innumerable) river gods. These included Achelous, the god of the Achelous River, the largest river in Greece, who gave his daughter in marriage to Alcmaeon and was defeated by Heracles in a wrestling contest for the right to marry Deianira; Alpheus, who fell in love with the nymph Arethusa and pursued her to Syracuse, where she was transformed into a spring by Artemis; and Scamander who fought on the side of the Trojans during the Trojan War and, offended when Achilles polluted his waters with a large number of Trojan corpses, overflowed his banks nearly drowning Achilles.
According to Hesiod, there were also three thousand Oceanids. These included Metis, Zeus' first wife, whom Zeus impregnated with Athena and then swallowed; Eurynome, Zeus' third wife, and mother of the Charites; Doris, the wife of Nereus and mother of the Nereids; Callirhoe, the wife of Chrysaor and mother of Geryon; Clymene, the wife of Iapetus, and mother of Atlas, Menoetius, Prometheus, and Epimetheus; Perseis, wife of Helios and mother of Circe and Aeetes; Idyia, wife of Aeetes and mother of Medea; and Styx, goddess of the river Styx, and the wife of Pallas and mother of Zelus, Nike, Kratos, and Bia.
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