But it is not the debased classical decoration alone which marks the illumination of the Carolingian school. The influence of the Celtic art, which has been described, imposed itself and combined with it. This combination was due to the Englishman, Alcuin of York, who became abbot of the Benedictine house of St Martin of Tours, and who did so much to aid Charlemagne in the revival of letters. Thus, in the finest examples of the Carolingian illuminated MSS., Celtic interlaced patterns stand side by side with the designs of classical origin; and, at the same time, it is interesting to observe that the older native Merovingian style of ornament makes its presence felt, now and again, in this or that detail. But with all the artistic effort bestowed upon it, it must be conceded that Carolingian illumination, as presented in the MSS., is not always pleasing. Indeed, it is often coarse and monotonous, and there is a tendency to conceal inferiority under a dazzling abundance of gold. The leading idea of the ornament of the great MSS. was splendour. Gold was used in profusion even in the writing of the text, and silver also in a minor degree; and the vellum, stained or painted purple, enhanced the gorgeous effect of the illumination. But undoubtedly the purer style of the Celtic school balanced and restrained the tendency to coarseness; and this foreign influence naturally was stronger in some centres than in others. For example, in the abbey of Saint-Denis, near Paris, if we may draw conclusions from surviving examples, the Celtic style was in great favour. Another peculiarity in the decoration of the Carolingian MSS. is the tendency of the artist to mix his styles, and to attach details on a small scale, such as delicate sprays and flourishes, and minute objects, to large-scale initial letters, as though he felt that grossness required a corrective contrast. The art became more refined under the immediate successors of Charlemagne, and under Charles the Bald it culminated. The most famous MSS. of the Carolingian school are the _Evangeliarium_, written and illuminated by the scribe Godescalc for Charlemagne in the year 787; the _Sacramentarium_ written for Drogon, son of Charlemagne and bishop of Metz; the Gospels of the emperor Lothair, once at Tours; the first Bible of Charles the Bald, presented by Count Vivien, abbot of St Martin of Tours; the second Bible, called the Bible of Saint Denis, in Franco-Saxon style; and the so-called Gospels of Francis II. There are also in the British Museum (Harleian MS. 2788) an Evangeliarium written in gold and known as the _Codex aureus_, of this school; and a Bible of Alcuin's recension, probably executed at Tours in the middle of the 9th century, with illustrative miniatures and initial letters, but of a less elaborate degree of ornament.