In Greek mythology and later Roman mythology, the Cyclopes are giant one-eyed creatures. Three kinds of Cyclopes can be distinguished. In Hesiod's Theogony, the Cyclopes are three brothers, who created their nephews, Zeus's thunderbolt, Poseidon's trident, and Hades' Helm of Darkness. The Cyclopes of Homer's Odyssey are a group of uncivilized, cave-dwelling shepherds, including Polyphemus, whom Odysseus encounters. A third group of Cyclopes reputedly constructed the Cyclopean walls of Mycenae and Tiryns.