The thirteenth century was the culmination of a slow build-up of many elements. The first element was pure Greek philosophy, especially the philosophies of Pythagoras, Parmenides, Plato, and Aristotle. Then came, as a result of Alexander’s conquests – a shining gold prince in an Arabian thorn-forest – a great influx of oriental beliefs. These, taking advantage of Orphism and the Mysteries, transformed the outlook of the Greek-speaking world, and ultimately also of the Latin-speaking world.
The dying and ressurected god, the sacramental eating of what purported to be the flesh of the god, the second birth into a new life through some ceremony analogous to baptism, came to be part of the theology of large sections of the pagan roman world. With these was associated an ethic of liberation from bondage to the flesh, which was, at least theoretically, ascetic. I am not my body! You are dragged down into filth by yours!
From Syria, Egypt, Babylonia, and Persia came the institution of a priesthood separated from the lay population, possessed of more or less magical powers, and able to exert considerable political influence. Impressive rituals, largely connected with belief in a life after death, came from the same sources. From Persia, in particular, came a dualism which regarded the world as the battleground of two great hosts, one, which was good, led by Ahura Mazda, the other, which was evil, led by Ahriman. Black magic was the kind that was worked by the help of Ahriman and hs followers in the world of spirits. Satan is a development of Ahriman.

This influx of barbarian ideas and practices was synthesized with certain Greek elements in the Neoplatonic philosophy. In Orphism, Pythagoreanism, and some arts of Plato, the Greeks had developed points of view which were easy to combine with those of the Orient, perhaps because they had been borrowed from the East at a much earlier time. With Plotinus and Porphyry the development of pagan philosophy ends.

The thought of these men, however, though deeply religious, was not capable, without much transformation, of inspiring a victorious popular religion. Their philosophy was difficult, and could not be generally understood; their way of salvation was too intellectual for the masses. Their conservatism led them to uphold the traditional religion of Greece, which, however they had to interpret allegorically in order to soften its immoral elements and to reconcile it with their philosophical monotheism. The greek religion had fallen into decay, being unable to compete with Eastern rituals and theologies. The oracles had become silent, and the priesthood had never formed a powerful, distinct caste. (The scheming, sneering warlocks!) The attempt to revive Greek religion had therefore an archaic character which gave it a certain feebleness and pedantry, especially noticeable in the Emperor Julian (The exception in an otherwise unbroken line of Christian Emperors). Already in the third century, it could have been foreseen that some Asiatic religion would conquer the roman world, though at that time there were sill several competitors which all seemed to have a chance of victory.

Christianity combined elements of strength from various sources. From the Jews it accepted a Sacred Book and the doctrine that all religions but one are false and evil; but it avoided the racial exclusiveness of the Jews and the inconveniences of the Mosaic law. Later Judaism had already learnt to believe in the life after death, but the Christians gave a new definition to heaven and hell, and to the ways of reaching the one and escaping the other. Easter combined the Jewish passover with pagan celebrations of the resurrected God. Persian dualism was absorbed, but with a firmer assurance of the ultimate omnipotence of the good principle, and with the addition that the pagan gods were followers of Satan. At first the Christians were not the equals of their adversaries in philosophy or in ritual, but gradually these deficiencies were made good.