The Constantinople tradition even permeated Mohammedan countries. Thus the entire mosaic decoration of the Koubet-es Sakra (or dome of the rock) and the El Aksa mosque, both in Jerusalem, were executed by Greek artists, invited to Jerusalem specifically for that purpose. Those from the Dome of the Rock date largely from c. 694, with portions from the reconstruction under Saladin in 1187. Those from El Aksa are principally of Saladin's time. Even in Cordova, Spain, Greek artists, brought there by Abd-er-Rahman III., decorated the mihrab of the Great Mosque with rich floral mosaics (929-961).
Although in Europe, Byzantine mosaic passed into decadence in the 13th and 14th centuries and finally disappeared, through the tremendous development of the magnificent school of Italian mural painters, in Constantinople and Greece, mosaic remained the dominant church decoration until the fall of Constantinople (1453)• The mosaics of the church of the convent of Daphni, near Athens (c. ioo), are interesting examples of the middle period. In Constantinople great areas of mosaics still remain in churches converted into mosques; only in two cases are these ex posed : one is a beautiful ribbed dome in the Fetihieh Djami, originally the church of Pammakaristos (12th century), the other, and more important example, is the rich 14th century decoration of the Kahrieh Djami, once the church of the Chora ; these show that in the 14th century the earlier hieratic stiffness of figure drawing, and the almost mechanical regularity of composition, decoratively so impressive, of the earlier period, was giving way to a much more pictorial ideal. There are not a few resemblances between some of the scenes here and the almost contemporary decoration in fresco of the church of St. Francis at Assisi. The borders and the ornamental details retain, however, their old character, and the gold ground, and the roughness of texture, still make these decorations essentially mosaic in character, and not the imitated paintings of the later work at St. Mark's at Venice.
Mediaeval Italian.—The opus sectile of Roman marble floors had an equally distinguished mediaeval development. This came through the combination of opus sectile, in which large slabs of coloured marble were cut to a pattern, with opus Alexan drinum, a form of mosaic consisting of many small pieces of mar ble cut to constant "stock" shapes. These shapes are: right angle and equilateral triangles, lunettes and squares, by the combina tion of which all sorts of geometric patterns could be obtained. The colours most common are red, dark green, white, black and occasionally creamy yellow. The most usual pattern is that ob
tained by inscribing in a large triangle, smaller triangles of al ternating dark and light colours. With opus Alexandrinum, con tinuous bands were formed which were inset into the opus sectile to make borders for panels, or running interlaces and guilloches (q.v.). The effect thus achieved of contrast of large and small scale was extremely impressive and there was an in definite supply of coloured marble to be had for the taking from pagan Roman buildings. The circles so frequently used were made by slicing Roman columns. The use of this type of pave ment is so common in Italy as to make it difficult to select ex amples; those of St. Mark's, Venice, and S. Maria Maggiore, S. Maria in Trastevere, and S. Clemente, all in Rome, are particu larly striking. The decorative possibilities of this combination of opus sectile and opus Alexandrinum were recognized during the 12th, 13th and 14th. centuries for the decoration of altar frontals, ambones, choir screens and parapets. Rome and south Italy are particularly rich in examples (see AMBO). Roman workers in this type of mosaic evidently travelled widely, for in Westminster abbey the space in front of the high altar was decorated with it in the third quarter of the 13th century by a Roman artist named Odericus.
In using opus Alexandrinum for church furniture a continual decrease in the size of the units, and an increased delicacy in the scale of the pattern was obtained. In this development it was but natural to substitute glass or enamel, in some cases, for the earlier marble, and it is this type which is known by the name of the family that, during the 13th century, was its chief exponent Cosmati work. Its use was not limited to flat surfaces. Fre quently the spiral columns, then so popular, had grooves cut in the hollow spiral flutes, which were filled with Cosmati mosaic of exquisite delicacy. This is the case in the 13th century cloisters of St. John Lateran and St. Paul Outside the Walls, both at Rome, in the paschal candlestick at S. Clemente, Rome, and in much church furniture in the south of Italy. Without doubt, work of this kind was common in the 13th century all over Europe and mosaic patterns probably exerted a large influence upon the other arts, especially in the case of enamel work on metal. In West minster abbey the shrine of Edward the Confessor (1269), and the tomb of Henry III. (1291), are both remarkable examples of rich Cosmati work outside of Italy; they were the work of one Peter, a Roman citizen, who was possibly a pupil of the Cosmati.