The walls of the propylons tapered from the base toward the top, and the same thing sometimes occurred in other walls. In almost all cases the stone walls are built of very large blocks, and they show an unrivaled skill in masonry. The roofing which remains is executed entirely in stone, but not arched or vaulted. The rock-cut tombs, however, contain ceilings of an arched shape, and in some cases forms which seem to be an imitation of timber roofing. The roofing of the hypostyle hall at Karnak provides an arrangement for admitting light very similar to the clerestory of gothic cathedrals. The openings were all covered by a stone lintel, and consequently were uniformly square-headed. The interspaces between columns were similarly covered, and hence Egyptian architecture has been, and correctly, classed as the first among the styles of trabeated architecture. Window openings seldom occur. The columns have been already described to some extent. They are almost always circular in plan, but the shaft is sometimes channeled. They are for the most part of sturdy proportions, but great grace and elegance are shown in the profile given to shafts and capitals. The design of the capitals especially is full of variety, and admirably adapts forms obtained from the vegetable kingdom. The general effect of the Egyptian column, wherever it is used, is that it appears to have, as it really has, a great deal more strength than is required. The fact that the abacus (the square block of stone introduced between the moulded part of the capital and what it carries) is often smaller in width than the diameter of the column aids very much to produce this effect. Mouldings are very rarely employed; in fact, the large bead running up the angles of the pylons, etc., and a heavy hollow moulding doing duty as a cornice, are all that are usually met with. Sculpture and carving occur occasionally, and are freely introduced in later works, where we sometimes find statues incorporated into the design of the fronts of temples. Decoration in color, in the shape of hieroglyphic inscriptions and paintings of all sorts, was profusely employed, and is executed with a truth of drawing and a beauty of coloring that have never been surpassed. Almost every object drawn is partly conventionalized, in the most skillful manner, so as to make it fit its place as a piece of a decorative system.