The apartments had no communication with one another, but usually opened into a court; and, as they were unprovided with windows, or apertures that served for them, the only light from without must have been admitted by the doorways. These were made with the sides approaching each other towards the top, so that the lintel was considerably narrower than the threshold, a peculiarity, also, in Egyptian architecture. The roofs have for the most part disappeared with time. Some few survive in the less ambitious edifices, of a singular bell-shape, and made of a composition of earth and pebbles. They are supposed, however, to have been generally formed of more perishable materials, of wood or straw. It is certain that some of the most considerable stone- buildings were thatched with straw. Many seem to have been constructed without the aid of cement; and writers have contended that the Peruvians were unacquainted with the use of mortar, or cement of any kind.28 But a close, tenacious mould, mixed with lime, may be discovered filling up the interstices of the granite in some buildings; and in others, where the wellfitted blocks leave no room for this coarser material, the eye of the antiquary has detected a fine bituminous glue, as hard as the rock itself.29 The greatest simplicity is observed in the construction of the buildings. which are usually free from outward ornament; though in some the huge stones are shaped into a convex form with great regularity, and adjusted with such nice precision to one another, that it would be impossible, but for the flutings, to determine the line of junction. In others, the stone is rough, as it was taken from the quarry, in the most irregular forms, with the edges nicely wrought and fitted to each other. There is no appearance of columns or of arches; though there is some contradiction as to the latter point. But it is not to be doubted, that, although they may have made some approach to this mode of construction by the greater or less inclination of the walls, the Peruvian architects were wholly unacquainted with the true principle of the circular arch reposing on its key-stone.30