The Christian basilica (see Figs. 67, 68) generally comprised a broad and lofty nave, separated by rows of columns from the single or double side-aisles. The aisles had usually about half the width and height of the nave, and like it were covered with wooden roofs and ceilings. Above the columns which flanked the nave rose the lofty clearstory wall, pierced with windows above the side-aisle roofs and supporting the immense trusses of the roof of the nave. The timbering of the latter was sometimes bare, sometimes concealed by a richly panelled ceiling, carved, gilded, and painted. At the further end of the nave was the sanctuary or apse, with the seats for the clergy on a raised platform, the _bema_, in front of which was the altar. Transepts sometimes expanded to right and left before the altar, under which was the _confessio_ or shrine of the titular saint or martyr. An _atrium_ or forecourt surrounded by a covered arcade preceded the basilica proper, the arcade at the front of the church forming a porch or _narthex_, which, however, in some cases existed without the atrium. The exterior was extremely plain; the interior, on the contrary, was resplendent with incrustations of veined marble and with sumptuous decorations in glass mosaic (called _opus Grecanicum_) on a blue or golden ground. Especially rich were the half-dome of the apse and the wall-space surrounding its arch and called the _triumphal arch_; next in decorative importance came the broad band of wall beneath the clearstory windows. Upon these surfaces the mosaic-workers wrought with minute cubes of colored glass pictures and symbols almost imperishable, in which the glow of color and a certain decorative grandeur of effect in the composition went far to atone for the uncouth drawing. With growing wealth and an increasingly elaborate ritual, the furniture and equipments of the church assumed greater architectural importance. A large rectangular space was retained for the choir in front of the bema, and enclosed by a breast-high parapet of marble, richly inlaid. On either side were the pulpits or _ambones_ for the Gospel and Epistle. A lofty canopy was built over the altar, the _baldaquin_, supported on four marble columns. A few basilicas were built with side-aisles, in two stories, as in S. Lorenzo and Sta. Agnese. Adjoining the basilica in the earlier examples were the baptistery and the tomb of the saint, circular or polygonal buildings usually; but in later times these were replaced by the font or baptismal chapel in the church and the _confessio_ under the altar. [Illustration: FIG. 67.--PLAN OF THE BASILICA OF ST. PAUL.]