Early Christian art marked a radical departure from the realism of the Greeks.  This attitude was dictated by the need for secrecy as well as by the new spirituality.  The paintings in the catacombs no longer reproduce natural appearance; the objects represented are now symbols which serve to divert the mind from the physical world to hidden meanings.  There are corporal images of things in the real world such as fishes, dolphins doves or lambs, but each is merely an arrow pointing to or suggesting something invisible.  The directness of realism has yielded to the indirectness of symbolism and the image is a way-station, which one passes by instead of dwelling upon it. It comes close to the hieroglyph.

The example of the fish is most striking. Here the symbol has a double meaning. The figure of the fish suggests its name, which in turn is a reference to the Lord, for it is an acrostic formed from the initial letters of "Jesus Christ, son of the Redeeming God,"

As late as the middle of the twelfth century, Suger, the illustrious Abbot of Saint-Denis, testified to the permanence of this trend toward the symbolic when he said to attend to the tangible, material realities, which are the objects of realism, is evidence only of the weakness of the spirit.  We must use these things, rather, as steppingstones in our ascent to the supreme Truth, which is beyond the reality of the senses and even of the intellect. The visual world has no reality save as a sign of and a way of access to the Invisible.

This tradition inaugurated by Plotinus, which had such a profound influence on St. Augustine, had a long life. Prior to the Romanesque period, it nourished Byzantine art, which, if only for geographical reasons, is closely linked with Eastern art.

The Church, particularly after the fifth and sixth centuries, favoured pictorial representations of Biblical history rather than the symbols used by the early Christians. Even so, the violent iconoclastic reaction of the ninth century came close to purging religious art of all its representational elements, as happened in Moslem civilization at about the same time. Although the paintings and mosaics of that period often told a story, they were not realistic, for the narrative was intended only as a framework for the "message" the work conveyed.

Early in the fifth century St. Nilus, writing to a high official of the Empire, ordered him to see to it that "those who do not know their letters and cannot read the Scriptures remember, when looking at pictures, the noble actions of those who faithfully served the true God and be encouraged to imitate their conduct." The resultant art, which, however far removed from realism, at least aims at representing something, does not do so out of an aesthetic conviction; it conceives of itself merely as a convenient means of attaining a religious end. It remains faithful to Plotinus' revealing injunction: "to open the eyes of the soul by closing those of the body."

This is why Byzantine art is not bound by natural appearance. Perfectly adapted to the requirements of its surface, instead of impressing the viewer with its skillful command of illusion, it exploits its materials—brilliant mosaics, glittering gold —fully, in order to overwhelm the soul with the splendour of light. This light, immaterial and yet visible, acts powerfully on our optical nerves, producing a fascination that is almost hypnotic, which is designed to lead the viewer directly to God.

The artist, following a path opposed to that of realism, has recourse to the material world only as a means to inducing the kind of contemplation in which the beholder sees "what is not a spectacle, but a form of vision, ecstasy," and which, according to the Enneads, is the goal of art. Such works appeal to the emotions rather than to the eye, seeking to project the soul upward into "an intimate union, not with the statue but with the Godhead itself..."

The mystics have always regarded light as the closest physical approximation to the Godhead; the later use, in the West, of stained-glass windows was occasioned by this religious significance of light. The stained-glass window transfigures reality rather than showing it; it gives to objects a radiance, makes them seem devoid of substance and inconceivably luminous, as though they belonged to another world. The stained-glass window takes the place of the mosaic in northern countries where the light is not strong enough merely to be reflected, as in mosaics, but must be fully conserved by being allowed to pass directly through the glass.