the symbols of the four Evangelists, while the remaining spaces contain representations of the Apostles; Crosses are represented on the ends also, with angels in various attitudes. 
Altar of the Fifth Century found at Auriol near Marseilles, France The famous reredos of St. Mark's, Venice, known as the Pala d'oro, which dates from the tenth century, was originally an antependium. To the following (eleventh) century belongs the splendid golden antependium presented to the Cathedral of Basle by the Emperor Henry II now in the Musée de Cluny at Paris. In five column arcades the figures of Our Lord, the Archangels Gabriel, Raphael, and Michael, and St. Benedict are represented. Such costly antependia as these were of course rare; the material more commonly used was wood, with representations of Christ or saints. A painted wooden panel, arcaded in a manner very similar to the antependium of Basle, is preserved in the episcopal museum of Münster in Westphalia. It dates from the twelfth century. Down to the tenth century the ciborium was in general use as a protection and ornamental feature of altars. The ciborium of Sant' Apollinare in Classe, Ravenna, which belongs to the early ninth century, is, as noted above, essentially the same as those of the earlier period. After the tenth century, however, except in Italy and the Orient, where ciboria were always in favour, they were rarely employed. The best example of a ciborium of the early Gothic period is in the Church of Our Lady of Halberstadt, Germany; two other Gothic ciboria are in the cathedrals of Ratisbon and Vienna. In Italy numerous medieval ciboria still exist. The early types of Christian altar, unlike those most in vogue during the Middle Ages, had no superstructure. So long, indeed, as the bishop's throne occupied the centre of the apse, a reredos (retabulum), which would conceal the bishop from the congregation, would have been impracticable. By degrees, as we have seen, the custom was introduced, with the general adoption of the Eastern apse of the celebrant facing in the same direction as the congregation, and it became possible to introduce an ornamental panel at the back of the altar similar to the antependium. Probably the custom of exposing relics on the altar, approved by Pope Leo IV (P.L., CXV, 677), exercised some influence on the development of the reredos, and the antependium naturally suggested its form. The reredos was introduced about the beginning of the twelfth century. The oldest existing example of it is the Pala d'oro of St. Mark's, Venice, which, after reconstruction, was detached from the front and placed at the back of the altar by the Doge Ordefalo Faliero, in 1105. The Church of Kloster-Neuburg, near Vienna, also contains a beautiful example of a twelfth-century reredos, with representations from the Old and the New Testament. The reredos of the thirteenth and fourteenth centuries was only moderately elevated when compared with the style which found favour in the late Gothic and Renaissance periods. The practice of exhibiting relics was, as we have seen, authorized in the ninth century, but not before the thirteenth century were reliquaries permanently kept on, or more frequently behind, the altar. In the latter case a platform was specially constructed for the purpose In some instances the reliquaries formed part of the reredos but the more common arrangement was to place them on a platform. This practice of permanently exposing relics behind the altar influenced certain other changes of importance with regard to the ciborium and the confessio. The latter feature now disappeared; there was no longer a reason for its existence, since the relics were provided with a new location; and the ciborium was modified into a baldacchino elevated above the reliquary back of the altar. An example of this arrangement, of the thirteenth century, may be seen in the chapel of the Blessed Virgin, in the church of St. Denis, Paris. At first only the altar of relics, usually placed at the end of the apse, was provided with a reredos, but in the course of the fourteenth century the main altar also was similarly provided.
Altar formerly placed in Abbey Church of St. Denis, Paris, XI Century
The comparative simplicity of the early reredos gradually yielded, in the course of the fourteenth, fifteenth, and sixteenth centuries, to the prevalent taste for richness of adornment, and reliquaries became of secondary consideration. The reredos now became a great structure, reaching in many instances to the vault of the church, containing life-sized statues of Our Lord, the Blessed Virgin, and the saints, besides a number of representations in relief of sacred subjects. This structure was usually of wood, carved or painted. It was connected with the altar by means of a predella, or altar-step, similar to the predella of modern altars, for candelabra, on which the Apostles or other saints were depicted. Towards the end of the sixteenth century the influence of the Renaissance effected another change in the form of the altar. Porticoes, modelled after the triumphal arches of antiquity, with statues in high and low relief, took the place of the reredos, and more costly materials, such as rare marbles, were employed in their construction. In the seventeenth and eighteenth centuries especially, altars of the Renaissance style became surcharged with ornamentation, often in bad taste and of inferior materials.
