Thus, for example, the existing mosaics on the west front of St Mark's Basilica in Venice[44], which were copied from noble paintings by Titian and Tintoretto, are immeasurably inferior to the earlier mosaics with stiff, hieratic forms designed after Byzantine models, as for example the mosaics in the Apse of SS. Cosmas and Damian in Rome, executed for Pope Felix IV. 526 to 530; see fig. 8. So, again, the skilfully drawn and modelled figures in a manuscript executed by Giulio Clovio in the sixteenth century are not worthy to be compared, for true decorative beauty and fitness, with the flat, rigid forms, full of dignity and simple, rhythmical beauty which we find in any Byzantine manuscript of a good period[45]. [Illustration: Fig. 8. Mosaic of the sixth century in the apse of the church of SS. Cosmas and Damian in Rome.] _Limitations of Byzantine Art._ It should, however, be remarked that in Byzantine art this conventional treatment of the human form is carried too far, and therefore, splendid as a fine Byzantine manuscript usually is, it falls far short of the almost perfect beauty that may be seen in Anglo-Norman and French illuminated manuscripts of the thirteenth and fourteenth centuries, such marvels of beauty, for example, as French manuscripts of the _Apocalypse_ executed in the first half of the fourteenth century in Northern France; see below, page 118. _Edict against statues._ Till the eighth century, Byzantine art, both in manuscripts and in other branches of art, continued to advance in technical skill, though little change or development of style took place. In the eighth century the iconoclast schism, fostered by the Emperor Leo III. the Isaurian, an uncultured and ignorant soldier who began by issuing an edict against image-worship in the year 726 A.D., gave a blow to Byzantine art which brought about a very serious decadence during the ninth and tenth centuries, more especially in Constantinople, which up to that time had been one of the chief literary and artistic centres of the Christian world. Pictures of all kinds, as well as statues, were destroyed by the iconoclast fanatics, and the cause of learning suffered almost as much as did the arts of painting and sculpture. _Frankish MSS._ One result of this schismatic outbreak was that Constantinople ceased to be one of the chief centres for the production of beautiful illuminated manuscripts, and various Frankish cities, such as Aix-la-Chapelle and Tours, took its place under the enlightened patronage of Charles the Great the Emperor of the West, who, in the second half of the ninth century, by the aid of the famous Northumbrian scholar and scribe Alcuin of York, brought about a wonderful revival of literature and of the illuminator's art in various cities and monasteries within the Western Empire. _Byzantine decadence._