The method of depicting designs by bringing together morsels of variously colored materials is of high antiquity. We are apt to think of a line of distinction between classical and Christian mosaics in that the former were generally of marble and the latter mostly of colored and gilt glass. But glass mosaics were already in use in the Augustan age, and the use of gilt tesserae goes back to the 1st or 2nd century. The first application of glass to this purpose seems to have been made in Egypt, the great glass-working centre of antiquity, and the gilding of tesserae may with probability be traced to the same source, whence, it is generally agreed, most of the gilt glass vessels, of which so many have been found in the catacombs, were derived. The earliest existing mosaics of a typically Christian character are some to be found at Santa Costanza, Rome (4th century). Other mosaics on the vaults of the same church are of marble and follow a classical tradition. It is probable that we have here the meeting-point of two art-currents, the indigenous and the eastern.
In Rome, the great apse-mosaic of S. Pudenziana dates from about A.D. 400. The mausoleum of Galla Placidia, Ravenna, is incrusted within by mosaic work of the 5th century, and most probably the dome mosaics of the church of St George, Salonica, are also of this period. Of the 6th century are many of the magnificent examples still remaining at Ravenna, portions of the original incrustation of St Sophia, Constantinople, those of the basilica at Parenzo, on the Gulf of Istria, and of St Catherines, Sinai. An interesting mosaic which is probably of this period, and has only recently been described, is at the small church of Keti in Cyprus. This, which may be the only Byzantine mosaic in the British dominions, fills the conch of a tiny apse, but is none the less of great dignity. In the centre is a figure of the Virgin with the Holy Child in her arms standing between two angels who hold disks marked with the sign χ. They are named Michael and Gabriel. Another mosaic of this period brought from Ravenna to Germany two generations ago has been recently almost rediscovered, and set up in the new Museum of Decorative Art in Berlin. In this, a somewhat similar composition fills the conch of the apse, but here it is the Risen Christ who stands between the two archangels.
Above, in a broad strip, a frieze of angels blowing trumpets stand on the celestial sea on either hand of the Enthroned Majesty.
Such mosaics flowed out widely over the Christian world trom its art centres, as far east as Sanâ, the capital of Yemen, as far north as Kiev in Russia, and Aachen in Germany, and as far west as Paris, and continued in time for a thousand years without break in the tradition save by the iconoclastic dispute. The finest late example is the well-known "mosaic-church" (the Convent of the Saviour) at Constantinople, a work of the 14th century.
The single figures were from the first, and for the most part, treated with an axial symmetry. Almost all are full front; only occasionally will one, like the announcing angel, be drawn with a three-quarter face. The features are thus kept together on the general map of the face. In the same way the details of a tree will be collected on a simple including form which makes a sort of mat for them. Groups, similarly, are closely gathered up into masses of balanced form, and such masses are arranged with strict regard for general symmetry. "The art," as Bayet says, "in losing something of life and liberty became so much the better fitted for the decoration of great edifices." The technical means were just as much simplified, and only a few frank colours were made sufficient, by skilful juxtaposition, to do all that was required of them. The fine pure blue, or bright gold, backgrounds on which the figures were spaced, as well as the broken surface incidental to the process, created an atmosphere which harmonized all together.
At St Sophia there were literally acres of such mosaics, and they seem to have been applied with similar profusion in the imperial palace.
Mosaic was only a more magnificent kind of painting, and painted design followed exactly the same laws; the difference is in the splendour of effect and in the solidity and depth of colour. Paintings, from the first, must have been of more grey and pearly hues. A large side chapel at the mosaic church at Constantinople is painted, and it is difficult to say which is really the more beautiful, the deep splendour of the one, or the tender yet gay colour of the other. The greatest thing in Byzantine art was this picturing of the interiors of entire buildings with a series of mosaics or paintings, filling the wall space, vaults and domes with a connected story. The typical character of the personages and scenes, the elimination of non-essentials, and the continuity of the tradition, brought about an intensity of expression such as may nowhere else be found. It is part of the limited greatness of this side of Byzantine art that there was no room in it for the gaiety and humour of the later medieval schools; all was solemn, epical, cosmic. When such stories are displayed on the golden ground of arches and domes, and related in a connected cycle, the result produces, as it was intended to produce, a sense of the universal and eternal.
Beside this great power of co-ordination possessed by Byzantine artists, they created imaginative types of the highest perfection. They clothed Christian ideas with forms so worthy, which have become so diffused, and so intimately one with the history, that we are apt to take them for granted, and not to see in them the superb results of Greek intuition and power of expression. Such a type is the Pantocrator, - the Creator-Redeemer, the Judge inflexible and yet compassionate, - who is depicted at the zenith of all greater domes; such the Virgin with the Holy Child, enthroned or standing in the conchs of apses, all tenderness and dignity, or with arms extended, all solicitude; of her image the Painter's Guide directs that it is to be painted with the "complexion the colour of wheat, hair and eyes brown, grand eyebrows, and beautiful eyes, clad in beautiful clothing, humble, beautiful and faultless"; such are the angels with their mighty wings, splendid impersonations of beneficent power; such are the prophets, doctors, martyrs, saints, - all have been fixed into final types.