The material employed for the external and internal face of the walls in a very large proportion of the buildings mentioned in this chapter is marble. This is sometimes used in blocks as stone is with us, but more frequently in the form of thin slabs as a facing upon masonry or brickwork. In Lombardy, where brick is the natural building material, most of the walls are not only built but faced with brick; and the ornamental features, including tracery, are often executed in ornamental brickwork, or in what is known as terra-cotta (_i.e._ bricks or blocks of brick clay of fine quality, moulded or otherwise ornamented and burnt like bricks). Stone was less commonly employed as a building material in Italy during the Gothic period, than in other countries of Europe. The surfaces of the vaults, and the surfaces of the internal walls were often covered with mosaics, or with paintings in fresco. Vaulting is frequently met with, but it is generally simple in character, the flat external roof over it is commonly covered with tiles or metal, while the apparent gable frequently rises more sharply than the actual roof. The Italians seem never to have cordially welcomed the Gothic principle of resisting the thrust of vaults or arches by a counter-thrust, or by the weight of a buttress. The buttress is almost unknown in Italian Gothic, and as a rule an iron tie is introduced at the feet of such arches as would in France or Germany have been buttressed. This expedient is, of course, economical, but to northern eyes it appears strange and out of place. The Italians, however, take no pains to conceal it, and many of their lighter works, such as canopies over tombs, porches, &c., would fall to pieces at once were the iron ties removed. Open timber roofs in the English fashion are unknown; but the wooden ceilings already alluded to are found in San Zeno at Verona, and the Eremitani at Padua. A kind of open roof of large span, carried by curved ribs and tied by iron ties, covers the great hall of the Basilica at Vicenza, and the very similar hall at Padua. The ribs of these roofs are built up of many thicknesses of material bolted together. The design of Italian Gothic buildings presents many peculiarities, some of which are due to the materials made use of. For example, where brick and terra-cotta are alone employed, wide moulded cornices of no great projection, and broad masses of enriched moulding encircling arches are easily executed, and they are accordingly constantly to be found; but bold mouldings, with deep hollows, similar to those of Early English arches, could not be constructed of these materials, and are not attempted. These peculiarities will be found in the Town Hall at Cremona, of which an illustration (Fig. 50) has already been given. [Illustration: FIG. 56.--WINDOW FROM TIVOLI.]