In the eighth century, the epoch at which the use of glass-windows was becoming general, the basilica of St. John Lateran and the Church of St. Peter at Rome possessed coloured glass-windows; and Charlemagne, who had caused mosaics of coloured glass to be made in a large number of churches, did not fail to avail himself of this kind of ornament in the cathedral erected by him at Aix-la-Chapelle. Up to this time the only method of making glass was in small pieces, generally round, and designated by the name of _cires_, a number of which by means of a network of plaster, wooden frames, or strips of lead, were used to fill up the windows. This material being, however, very costly, it could only be introduced into edifices of great importance. Added to this, it can scarcely be a source of wonder if, at a time when all branches of art had relapsed into a sort of barbarism, and glass was only exceptionally employed in ordinary purposes, no one thought of decorating it with painted figures and ornaments. With regard to mosaic, either in marble or coloured glass, Martial, Lucretius, and other writers of antiquity, mention it in their works. Egypt had a knowledge of it even before Greece; the Romans were accustomed to employ it in ornamenting the roofs and pavement of their temples, and even their columns and streets. Some magnificent specimens of these decorations have remained to our time, and they are considered as inseparable from the architecture of the emperors. Some have desired to attribute the custom of employing coloured glass in mosaics to the rarity of coloured marbles. Would it not be a more probable hypothesis that the simultaneous use of marble and glass for this purpose was the result of improvements in the art of making mosaics? for glass that, by metallic mixtures, may be brought to a variety of colours, is much more easily adapted to pictorial combinations than marble, the tints of which are the result of the caprices of nature. Seneca, alluding to the use of coloured glasses in mosaic, complains of people not being able “to walk except on precious stones;” this shows how prevalent the use of rich mosaics had become in Rome. But this art must have singularly fallen into decay, for the few examples of the kind we now possess, which date from the first centuries of Christianity, are marked with a character of simplicity that fully harmonises with the rudeness of the artists of those times. Among these specimens must be mentioned a pavement discovered at Rheims, upon which are represented the twelve signs of the zodiac, the seasons of the year, and Abraham’s Sacrifice; another on which are depicted Theseus and the labyrinth of Crete, in juxtaposition with David and Goliath. It is, moreover, known that there existed in the Forum of Naples a portrait in mosaic of Theodoric, king of the Goths, who had caused a representation of the Baptism of Christ to be executed, in the church of Ravenna, by the same process.