The naves of Italian churches rarely show the division into three, common in the north. The triforium is almost invariably absent, and the clerestory is often reduced to a series of small round windows, sufficient to admit the moderate light which, in a very bright climate, is grateful in the interior of such a building as a church; but they are far less effective features than our own well-marked clerestory windows. [Illustration: FIG. 54.--OGIVAL WINDOW-HEAD.] The doorways are often very beautiful, and are frequently sheltered by projecting porches of extreme elegance and lightness. The window openings are, as a rule, cusped. An ogee-shaped arch (Fig. 54) is constantly in use in window-heads, especially at Venice, and much graceful design is lavished on the arched openings of domestic and secular buildings. A great deal of the tracery employed is plate tracery.[27] The tracery in terra-cotta has already been referred to. In the large windows of the principal apartments and other similar positions of the palaces in Venice and Vicenza, a sort of tracery not met with in other countries is freely employed. The openings are square-headed, and are divided into separate lights by small columns; the heads of these lights are ogee-shaped, and the spaces between them and the horizontal lintel are filled in with circles, richly quatrefoiled or otherwise cusped (Fig. 55). The upper arcade of the Ducal Palace at Venice offers the best known and finest example of this class of tracery. [Illustration: FIG. 55.--TRACERY, FROM VENICE.] _Roofs and Vaults._ The vaulting of Italian churches is always simple, and the bays, as has been pointed out, are usually wider than those of the northern Gothic churches. Frequently there are no ribs of any sort to the groins of the vaults. A characteristic feature of Italian Gothic is the central dome. It is rarely very large or overpowering, and in the one instance of a magnificent dome--the Cathedral at Florence, the feature, though intended from the first, was added after the Gothic period had closed. Still many churches have a modest dome, and it frequently forms a striking feature in the interior, while in some northern instances (_e.g._ at the Certosa at Pavia, or at Chiaravalle) it is treated like a many storeyed pyramid and becomes an external feature of importance. At Sant' Antonio at Padua there are five domes. The churches of the preaching orders are some of them covered by timber ceilings, not perfectly flat but having an outline made up of hollow curves of rather flat sweep. The great halls at Padua and Vicenza displayed a vast wooden curved ceiling resembling the hull of a ship turned upside down. The ordinary church roof is of flat pitch and frequently concealed behind a parapet. Dormer windows, crestings, and other similar features, by the use of which northern architects enriched their roofs, are hardly ever employed by Italian architects. _Mouldings and Ornaments._