In ancient Greek mythology, the Styx formed a boundary between the world of the living and the underworld.
The Styx was both a river and a powerful underworld deity in Greek myth. Gods were said to swear binding oaths by the river, and breaking such an oath carried severe consequences. This sacred status made the Styx more than a simple geographical feature of Hades.
Later retellings often present the Styx as the principal river separating ordinary life from the realm of the dead. Charon, the ferryman, is more commonly linked in classical art and literature with the Acheron, although traditions about the underworld’s rivers vary across authors and periods.
The Styx is also distinct from Lethe, whose waters were associated with forgetfulness, and Phlegethon, a river of fire. These rivers can appear together in accounts of Hades, so naming the specific function is important.