_The Plan or floor-disposition_ of the basilican churches, as has been pointed out, was distinctive. The atrium, or forecourt, the porch, the division into nave and aisles; the transept, the great arch, and the apse beyond it with the episcopal seat at the back behind the altar; the ambos; and the enclosure for the choir, were typical features. Detached towers sometimes occurred. The plan of Romanesque churches was based upon that of the basilica; the atrium was often omitted, so was the transept sometimes; but, when retained, the transept was generally made more prominent than in the basilica. The position of the altar and of the enclosure for the choir were changed, but in other respects the basilica plan was continued. In Germany, however, apsidal transepts (Fig. 178) were built. Towers were common, occasionally detached, but more frequently joined to the main building. [Illustration: FIG. 178.--PLAN OF THE CHURCH OF THE APOSTLES AT COLOGNE.] Circular and polygonal buildings for use as baptisteries, and sometimes as churches, existed both in the basilican and the Romanesque time. Byzantine church plans are all distinguished by their great central square space, covered by the central dome, flanked usually by four arms, comparatively short, and all of equal length; and the plan of the buildings is generally square, or nearly so, in outline. Circular and polygonal buildings sometimes occur. [Illustration: FIG. 179.--SPIRE OF SPIRES CATHEDRAL.] Few traces of the arrangement of military, secular, or domestic buildings earlier than the twelfth century remain, but some examples of a cloister at the side of the nave (generally the south side) of a church, giving or intended to give access to monastic buildings, still exist. _The Walls_ of such buildings as have come down to us are, it may be well understood, strong, since the most recent of this round-arched series of buildings must be about seven hundred years old. Fine masonry was not much employed till the time of the Normans, but the Roman plan of building with bricks or rubble and casing the face of the walls with marble or mosaic, or at least plaster, was generally followed. The walls are carried up as gables and towers to a considerable extent (Fig. 179), especially in Western countries. _The Roof._--In a basilica this was of timber, in a Byzantine church it consisted of a series of domes; in a Romanesque church it was sometimes of timber as in the basilica, but not unfrequently vaulted. As a general rule the vault prevailed in the West and the dome in the East; and such examples of either sort of roof as occur in those provinces where the other was usual, like the domed churches in parts of France, must be looked upon as exceptional.