Five main rivers are traditionally said to flow through the Greek underworld.
The standard list consists of Styx, Acheron, Cocytus, Phlegethon, and Lethe. Each river carries a distinctive association: Styx is linked with hatred and divine oaths, Acheron with sorrow, Cocytus with lamentation, Phlegethon with fire, and Lethe with forgetfulness.
These rivers were not described identically in every ancient source. Homer mentions several underworld waters, while later writers such as Plato and Virgil developed or rearranged the geography. In some accounts, the dead cross the Styx; in others, Charon ferries them across the Acheron. Oceanus, the world-encircling river, and Eridanos can also appear in broader traditions, which explains why different counts sometimes arise.
Five remains the conventional quiz and reference answer. The rivers should not be confused with the judges of the dead or the regions of Hades, such as Tartarus and Elysium.