In ancient Greek mythology, the river Lethe caused the dead to forget their earthly lives.
Lethe was both a river of the underworld and a personification of forgetfulness. Souls who drank its water lost their memories. In some ancient and later accounts, forgetting was part of the normal process of entering a new existence; in others, memory and choice play a role in philosophical ideas about reincarnation.
Plato’s Republic includes the River of Forgetfulness in the Myth of Er. In that story, souls drink from the plain of Lethe before returning to embodied life, although the amount they drink affects what they remember. Orphic and related traditions sometimes emphasize the opposite river, Mnemosyne, whose water preserved memory and could be chosen by initiates.
Lethe is often confused with the Styx, but their roles differ. The Styx is associated with divine oaths and boundary-crossing, while Lethe specifically represents forgetfulness.