Among the most famous and sinister of the subterranean streams of antiquity were the dark waters of Cocytus, Acheron, Pyriphlegethon, and Styx.[122] These were the streams of the nether world, the world of the dead. Belief in the subterranean position of the after-world, the Hades of the Greeks, the Inferi of the Italian folk, was widespread and lasting among early Mediterranean peoples. Hellenic mythology placed not only Tartarus, the abyss of torment, but also the Elysian Fields in the depths. Plato taught that within the bowels of the earth are immense caverns, some filled with fire, some with water, others the abode of the shades. To be sure, rationalistic arguments against such doctrines were raised by the incredulous. Aristotle had believed that of all four elements the earth is the most dense and solid and that its position is at the center of the universe. Although the earth might be seamed with small water channels, it would be a reversal of the physical laws of the universe to suppose that within it there could exist caverns large enough to “hold Tartarus, the Elysian Fields, and the infinite multitude of the dead” (Cumont).[123] Hence some would identify the Elysian Fields with the Islands of the Blessed, placing them in the antipodes, and would relegate Tartarus to the lowest hollow of the celestial sphere.[124] But even this explanation could not be reconciled with the more mature cosmography of the Alexandrian age. The Epicureans resorted to out-and-out disbelief in a future life and future dwelling place of the spirit.[125] Others looked for the shades in the atmosphere below the moon’s orbit or else treated the whole problem in a lofty vein of allegory. Rationalistic questioning of the subterranean position of the next world, however, did not shake faith in this doctrine as it persisted among the ignorant, and the doctrine was given new life, if in somewhat different forms, by the Neoplatonic movement and the influx of Oriental cults during the waning years of the Western Empire.[126] The Neoplatonists reverted to Plato’s theory that the interior of the earth may well include hollows large enough to contain the future abode of men’s souls. The religion of Mithras tended to spread throughout the Occident the dualistic cosmology of an eternal conflict between the powers of light and goodness on high and the powers of darkness and evil below. In the words of Franz Cumont, whose truly fascinating study of this subject we are here following: Oriental dualism cut “the abode of the souls into two halves, of which it placed one in the luminous sky and the other in subterranean darkness. This was also the conception which, after some hesitation, became generally accepted by the Church and which for long centuries was to remain the common faith of Christendom.”[127] In the period with which it is our special problem to deal, then, we shall find that Hell is almost invariably placed in the heart of the earth.[128]