The myth occupies Republic Book X, 614b to 621d. Er, son of Armenius, is killed in battle, remains undecomposed, and revives twelve days later to describe judgment of souls, a thousand-year cycle of reward and punishment, the spindle of Necessity, the choice of new lives, and the drinking at the river Ameles in the plain of Lethe before rebirth. Plato frames it explicitly as a saved tale that could save us.
Scholars split on whether Plato borrowed Er from Orphic or Pythagorean tradition, invented him outright, or adapted a tale already circulating. His name puns in Greek, and Proclus, Macrobius, and late antique commentators treated the myth as a serious cosmology rather than ornament.
Modern readers in the survival-research tradition note that Er's account is structurally an NDE: bodily death, an out-of-body tour, a return with a message. They ask whether Plato was recording an experience type rather than inventing an allegory.
If the oldest great NDE narrative in Western literature ends with everyone forgetting everything on purpose, what exactly is the lesson we were meant to remember?