Thus the religion of the golden age of Greece was an anthropomorphic polytheism, closely connected with the life of the city-state, but relieved here and there by practices intended to provide more direct contact with the divine or bestow special blessing upon individuals.
The religion of Greece was finally undermined by at least three agencies.
In the first place, philosophy tended to destroy belief in the gods. The philosophic criticism of the existing religion was partly theoretical and partly ethical. The theoretical criticism arose especially through the search for a unifying principle operative in the universe. If the manifold phenomena of the universe were all reduced to a single cause, the gods might indeed still be thought of as existing, but their importance was gone. There was thus a tendency either toward monotheism or else toward some sort of materialistic monism. But the objections which philosophy raised against the existing polytheism were ethical as well as theoretical. The Homeric myths were rightly felt to be immoral; the imitation of the Homeric gods would result in moral degradation. Thus if the myths were still to be retained they could not be interpreted literally, but had to be given some kind of allegorical interpretation.
This opposition of philosophy to the existing religion was often not explicit, and it did not concern religious practice. Even those philosophers whose theory left no room for the existence or at least the importance of the gods, continued to engage loyally in the established cults. But although the superstructure of religion remained, the foundation, to some extent at least, was undermined.
In the second place, since religion in ancient Greece had been closely connected with the city-states, the destruction of the states brought important changes in religion. The Greek states lost their independence through the conquests of Philip of Macedon and Alexander the Great. Those conquests meant, indeed, a wide extension of Greek culture throughout the eastern world. But the religion of Alexander's empire and of the kingdoms into which it was divided after his death was widely different from the religion of Athens in her glory. Cosmopolitanism brought mighty changes in religion, as in the political sphere.
In the third place, the influence of the eastern religions made itself more and more strongly felt. That influence was never indeed dominant in the life of Greece proper so completely as it was in some other parts of the world. But in general it was very important. When the Olympic gods lost their place in the minds and hearts of men, other gods were ready to take their place.
Before any account can be given of the eastern religions taken separately, and of their progress toward the west, it may be well to mention certain general characteristics of the period which followed the conquests of Alexander. That period, which extended several centuries into the Christian era, is usually called the Hellenistic age, to distinguish it from the Hellenic period which had gone before.
The Hellenistic age was characterized, in the first place, by cosmopolitanism. Natural and racial barriers to an astonishing extent were broken down; the world, at least the educated world of the cities, was united by the bonds of a common language, and finally by a common political control. The common language was the Koiné, the modified form of the Attic dialect of Greek, which became the vehicle of a world-civilization. The common political control was that of the Roman Empire. On account of the union of these two factors, inter-communication between various nations and races was safe and easy; the nations were united both in trade and in intellectual activity.
With the cosmopolitanism thus produced there went naturally a new individualism, which extended into the religious sphere. Under the city-state of ancient Greece the individual was subordinated to the life of the community. But in the world-empire the control of the state, just because it was broader, was at the same time looser. Patriotism no longer engrossed the thoughts of men. It was impossible for a subject of a great empire to identify himself with the life of the empire so completely as the free Athenian citizen of the age of Pericles had identified himself with the glories of his native city. Thus the satisfactions which in that earlier period had been sought in the life of the state, including the state-religion, were in the Hellenistic age sought rather in individual religious practice.