There was a time when God directed the revolutions of the world, but at the completion of a certain cycle he let go; and the world, by a necessity of its nature, turned back, and went round the other way. For divine things alone are unchangeable; but the earth and heavens, although endowed with many glories, have a body, and are therefore liable to perturbation. In the case of the world, the perturbation is very slight, and amounts only to a reversal of motion. For the lord of moving things is alone self-moved; neither can piety allow that he goes at one time in one direction and at another time in another; or that God has given the universe opposite motions; or that there are two gods, one turning it in one direction, another in another. But the truth is, that there are two cycles of the world, and in one of them it is governed by an immediate Providence, and receives life and immortality, and in the other is let go again, and has a reverse action during infinite ages. This new action is spontaneous, and is due to exquisite perfection of balance, to the vast size of the universe, and to the smallness of the pivot upon which it turns. All changes in the heaven affect the animal world, and this being the greatest of them, is most destructive to men and animals. At the beginning of the cycle before our own very few of them had survived; and on these a mighty change passed. For their life was reversed like the motion of the world, and first of all coming to a stand then quickly returned to youth and beauty. The white locks of the aged became black; the cheeks of the bearded man were restored to their youth and fineness; the young men grew softer and smaller, and, being reduced to the condition of children in mind as well as body, began to vanish away; and the bodies of those who had died by violence, in a few moments underwent a parallel change and disappeared. In that cycle of existence there was no such thing as the procreation of animals from one another, but they were born of the earth, and of this our ancestors, who came into being immediately after the end of the last cycle and at the beginning of this, have preserved the recollection. Such traditions are often now unduly discredited, and yet they may be proved by internal evidence. For observe how consistent the narrative is; as the old returned to youth, so the dead returned to life; the wheel of their existence having been reversed, they rose again from the earth: a few only were reserved by God for another destiny. Such was the origin of the earthborn men.