In Greek mythology, Styx (; Ancient Greek: Στύξ [stýks]) is a goddess and a river that forms the boundary between Earth (Gaia) and the Underworld. The rivers Acheron, Cocytus, Lethe, Phlegethon, and Styx all converge at the centre of the underworld on a great marsh, which sometimes is also called the Styx. According to Herodotus, the river Styx originates near Pheneus. Styx is also a goddess with prehistoric roots in Greek mythology as a daughter of Tethys, after whom the river is named and because of whom it had miraculous powers.