But the poet also gives us precious hints as to the lot reserved for the soul in the interval between its incarnations. For palingenesis, unlike the doctrine of perpetual reincorporation, left a place for chastisement in the infernal regions. These were however situated, as we have seen, for the Pythagoreans and Posidonius, whom Virgil interpreted, not on earth but in the air. It was there that the soul had to purify itself from the stains acquired while it was in touch with the flesh. This pollution, we know,[454] was conceived in a very material form. The texts speak of a thickening of the subtle substance of which the soul is formed, of concretions encrusting it, of indelible marks with which the vices stain it. When the soul left the corpse, of which it kept the form, it first, as we have seen, floated in the ambient air. When it was not weighed down by the matter with which it had become impregnated, the breath of the atmosphere raised it gently and, gradually warming it, bore it to the heavens, and this is why the Winds are often represented on tombstones.[455] But these Winds, fierce divinities, could also cause the soul to expiate its faults bitterly. If it had lost its purity and lightness, the whirlwinds drew it into their vortex, the storms rolled and buffeted it, thus violently tearing away the crust which had become attached to it. The souls were thus freed from defilements contracted during life just as linen hung in the air is bleached and loses all odour. Their passage through the air did not complete their purification. In the East the idea was old that above the firmament was found the great reservoir of the waters which fell to the ground as rain. Beyond, a burning zone must extend, where the heavenly bodies were lit, and a river of fire, identified with the Pyriphlegethon of the Greeks, was imagined. These old mythological ideas were brought into relation with Stoic physics: above the region of the winds stretched that of the clouds, in which the rain, the snow and the hail were formed, and higher still there was the burning air, in which the lightning flashed and which touched the starry spheres. The souls must blaze a path through these obstacles. After being tossed and blown about by the winds, they were drenched by rain and plunged into the gulf of the upper waters. They reached at last the fires of heaven, of which the heat scorched them. Not till they had undergone this threefold trial, in the course of which they had passed through countless years of expiation, did they at length find peace in the serenity of the luminous ether.[456] Virgil,[457] in the passage already quoted, alludes to this doctrine when, in speaking of the souls, he says: “... Aliae panduntur inanes Suspensae ad ventos, aliis sub gurgite vasto Infectum eluitur scelus, aut exuritur igni.”