In Greek mythology, Tethys (Greek Τηθύς), daughter of Uranus and Gaia was an archaic Titaness and aquatic sea goddess, invoked in classical Greek poetry but not venerated in cult. Tethys was both sister and wife of Oceanus. She was mother of the chief rivers of the world known to the Greeks, such as the Nile, the Alpheus, the Maeander, and about three thousand daughters called the Oceanids. Considered as an embodiment of the waters of the world she also may be seen as a counterpart of Thalassa, the embodiment of the sea.
Although these vestiges imply a strong role in earlier times, Tethys plays virtually no part in recorded Greek literary texts, or historical records of cults. Walter Burkert notes the presence of Tethys in the episode of Iliad XIV that the Ancients called the "Deception of Zeus", where Hera, to mislead Zeus, says she wants to go to Oceanus, "origin of the gods" and Tethys "the mother". Burkert sees in the name a transformation of Akkadian tiamtu or tâmtu, "the sea," which is recognizable in Tiamat. Alternatively, her name may simply mean "old woman"; certainly it bears some similarity to ἡ τήθη, meaning "grandmother", and she is often portrayed as being extremely ancient (cf. Callimachus, Iamb 4.52, fr. 194).
Roman mosaic of Tethys from Antioch, Turkey
One of the few representations of Tethys that is identified securely by an accompanying inscription is the Late Antique (fourth century CE) mosaic from the flooring of a thermae at Antioch, now at the Harvard Business School in Boston, Massachusetts after being moved from Dumbarton Oaks. In the Dumbarton Oaks mosaic, the bust of Tethys—surrounded by fishes—is rising, bare-shouldered from the waters. Against her shoulder rests a golden ship's rudder. Gray wings sprout from her forehead, as in the mosaics illustrated above and below.
During the war against the Titans, Tethys raised Hera as her step-child, but there are no records of active cults for Tethys in historic times.
Tethys has sometimes been confused with another sea goddess who became the sea-nymph Thetis, the wife of Peleus and mother of Achilles during Classical times. Some myths imply a second generation relationship between the two, a grandmother and granddaughter.
Indicative of the power exercised by Tethys, one myth relates that the prominent goddess of the Olympians, Hera, was not pleased with the placement of Callisto and Arcas in the sky, as the constellations Ursa Major and Ursa Minor, so she asked her nurse Tethys to help. Tethys, a marine goddess, caused the constellations forever to circle the sky and never drop below the horizon, hence explaining why they are circumpolar. Robert Graves interprets the use of the term nurse in Classical myths as identifying deities who once were goddesses of central importance in the periods before historical documentation.
Tethys, a moon of the planet Saturn, and the prehistoric Tethys Ocean are named after this goddess.