<P> The idea of purgatory has roots that date back into antiquity . A sort of proto - purgatory called the "celestial Hades" appears in the writings of Plato and Heraclides Ponticus and in many other pagan writers . This concept is distinguished from the Hades of the underworld described in the works of Homer and Hesiod . In contrast, the celestial Hades was understood as an intermediary place where souls spent an undetermined time after death before either moving on to a higher level of existence or being reincarnated back on earth . Its exact location varied from author to author . Heraclides of Pontus thought it was in the Milky Way; the Academicians, the Stoics, Cicero, Virgil, Plutarch, the Hermetical writings situated it between the Moon and the Earth or around the Moon; while Numenius and the Latin Neoplatonists thought it was located between the sphere of the fixed stars and the Earth . </P> <P> Perhaps under the influence of Hellenistic thought, we find another intermediate state entering Jewish religious thought in the last centuries B.C.E. In Maccabees we find the practice of prayer for the dead with a view to their after life purification a practice accepted by some Christians . The same practice appears in other traditions, such as the medieval Chinese Buddhist practice of making offerings on behalf of the dead, who are said to suffer numerous trials . Among other reasons, Catholic belief in purgatory is based on the practice of prayer for the dead . </P>

Where does the idea of purgatory come from