In Greek mythology, the "River Styx" (Greek: Στύξ) was a river which forme the boundary between Earth and the Underworld (Hades). It circles Hades nine times. The rivers Styx, Phlegethon, Acheron and Cocytus all converge at the center of Hades on a great marsh. The other important rivers of Hades are Lethe and Eridanos. Styx was guarded by Phlegyas, who passes the souls from one side to another of the river. In other versions, Phlegyas guarded Phlegethon, one of the other main rivers of Hades. Sometimes the ferryman was called Charon.