In Greek mythology, Lethe was the Underworld river whose waters caused forgetfulness.
The name Lethe comes from a Greek word associated with concealment and oblivion. Souls who drank from the river were said to lose their memories, helping them become detached from their previous lives before reincarnation or continued existence in the Underworld.
Lethe is not the same as Styx, the river most famous for the gods’ binding oaths. Acheron is associated with sorrow and the passage of the dead, while Phlegethon is a river of fire in descriptions of the Underworld. These rivers often overlap in later summaries, so their functions can be confused.
Orphic and philosophical traditions sometimes describe an alternative river, Mnemosyne, whose waters preserved memory. Initiates were instructed to choose Mnemosyne rather than Lethe in certain afterlife beliefs. Thus Lethe represents forgetting, while Mnemosyne represents remembrance.