The Acheron is a river that stems in the Tomaros mountains in Epirus, north west Greece. Acheron translates as "river of woe" and is believed to be a branch of the underworld river Acheron over which in ancient Greek mythology Charon ferried the newly-dead souls across into Hades.
Greeks settled in Italy identified the Acherusian lake into which Acheron flowed with Lake Avernus.
Plato in his Phaedo identified Acheron as the second greatest river in the world, excelled only by Oceanus. He claimed that Acheron flowed in the opposite direction from Oceanus beneath the earth under desert places.
The word is also occasionally used as a synecdoche for Hades itself.
Virgil mentions Acheron with the other infernal rivers in his description of the underworld in Book VI of the Aeneid.
In Dante's Inferno, the Acheron river forms the border of Hell, in the Ante-Inferno. Following Greek mythology, Charon ferries souls across this river to Hell.