SOLAR THEOLOGY. - Solar theology is the last form that the religious thought of Greek-Roman paganism assumes before its definitive decline. In it converge the four fundamental lines of the religious picture of the Empire: the imperial cult, the mysteries, the cults of the East and the philosophical currents culminating in Neoplatonism.
Solar theology is the fruit of the astronomical science of the Chaldeans, which reached the West through the filter of Stoic thought. According to Babylonian astronomy, the sphere of the sun occupies the fourth place, which is the middle position, among the seven concentric spheres of the planets: at the center of the whole system lies the earth, motionless. From the sun depends the harmonious reality of the celestial movements; from it comes the rhythm of terrestrial life, thanks to its heat, which has active force and repulsive force like the heart in the human organism; from it depends also the rhythm of human events, which it regulates indirectly through the planets, its satellites. It is therefore an "intelligent light" (ὅς νυχόν; mens mundi; Cicero, De rep., VI, 4), and as such it also directs the human microcosm. The soul of man is likewise of a solar nature, while the body depends on the moon. The irradiation of the sun imprisons in the body incandescent particles that animate it. At the moment of death the heat of the sun reabsorbs with itself the soul-reason, while the soul-breath or psyche goes to the moon. Because of this astronomical pantheism, which deifies the world rather than the creator of the world, as Philo of Alexandria observed, the solar theology of the Chaldeans pleased the Stoics because it corresponded in substance to their hylozoism. And once it had entered the Western world and been elaborated by Hellenistic culture, it was destined to become the most valid exponent of the widespread syncretism of the time and to constitute the religious synthesis of paganism in the face of Christian thought.
All the Latin, Greek and Oriental gods in vogue in the Greek-Roman world end up being considered as so many aspects of the same divinity, while still maintaining the external variety of types, which could not be suppressed because they were too closely bound to tradition. This supreme divinity, which the crowd intuited as a force manifesting itself through the various divine specifications, and which cultivated minds felt as Intelligence, was bound to be concentrated in the sun, the most grandiose manifestation of the cosmos, the highest symbol of the Supreme Being in the various aspects of its divine attributes. The Neoplatonism of Julian the Apostate considers the imperial sun as an image of the intelligent sun (ὅς νυχόν), which is in turn a reflection of the ineffable One, the supreme and absolute Good. The intelligent sun therefore has the office of intermediary between the unreachable One and the sensible world. Because of this office of mediator, the sun is entitled to hegemony over all the other gods, who are merely its aspects, whether they be called Jupiter, Pluto, Serapis, Mithras, Bacchus or Apollo, who is the god that best expresses its essence.