A cyclops in Greek mythology and later Roman mythology, was a member of a primordial race of giants, each with a single eye in the middle of his forehead. The name is widely thought to mean 'circle-eyed'. Hesiod described one group of cyclopes and the epic poet Homer described another, though other accounts have also been written by the playwright Euripides, poet Theocritus and Roman epic poet Virgil. In Hesiod's Theogony, Zeus releases three Cyclopes, the sons of Uranus and Gaia, from the dark pit of Tartarus. They provide Zeus' thunderbolt, Hades' helmet of invisibility, and Poseidon's trident, and the gods use these weapons to defeat the Titans. In a famous episode of Homer's Odyssey, the hero Odysseus encounters the Cyclops Polyphemus, the son of Poseidon and Thoosa (a nereid), who lives with his fellow Cyclopes in a distant country.