A river surrounding the Underworld of Hades. Dead souls were ferried across it from the land of the living.
Styx was revered by the Olympians because she helped Zeus in his victory over the Titans, even though she was married to the Titan Pallas. If an oath was sworn in her name, it bound the gods to their promise. Ghosts floated over the gray waters, and corpses of those who had not paid their fare into the underworld floated along beside the boat of Charon, begging to be let on, as it carried the souls of those who did pay. Charon was restricted from helping unpaid souls.
When Psyche was sent to the Underworld on an untold mission by Venus, three women were deceivingly placed on the banks as Psyche got off the boat. They pretended to weave clothing and asked for assistance. Psyche resisted their persuasion and escaped the Underworld. Orpheus and Aeneas were two others who had triumphed in crossing the river and rejoining the land of the living. Aeneas was instructed by the Cumaean Sibyl to arrive at the Golden Bough so he could return from the Underworld.
Extra Notes: The Ferryman, Charon