“Forgetfulness” the Water of Oblivion in the Greek underworld, a spring giving rise to the River Lethe. According to the Orphics and other mystery-cultists, the spring of Lethe under a white cypress was the first thing seen in the underworld by the soul of the dead, which was very thirsty and would be tempted to drink from it. Part of the training of the mystery-cultists was the endurance of thirst, because one drink from the spring of Lethe caused complete oblivion of memories of past incarnations and leave them no wiser that the rest of humanity, always born without remembering previous lives. It was taught that the Enlightened Ones should always seek the spring of Memory (Mnemosyne). “Thou shalt find to the left of the house of Hades , and by the side thereof a white cypress. To this spring approach not near. But thou shalt find another, from the Lake of Memory cold water flowing forth, and there are guardians before it.”
The location of Lethe in the underworld, in classical and Gnostic imagery, originates from the oracle cave of Earth-deities (Chthonioi) at Lebadeia, where an individual made elaborate preparations to enter down into the dark pit to learn his fate through “things seen” or “things heard.” Among the preparations, “he has to drink of the water of Lethe, in order to achieve forgetfulness of all that he has hitherto thought of; and on top of it another water Mnemosyne, which gives him remembrance of what he sees when he has gone down.”
Classical writers made Lethe one of the principle rivers of the underworld, along with Acheron, Cocytus, Phegethon, and Styx. A.G.H.