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 well-fitted 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 [Footnote 28: Among others, see Acosta, lib. 6, cap. 15. - Robertson, History of America, (London, 1796,) vol. III. p. 213.] [Footnote 29: Ondegardo, Rel. Seg., Ms. - Ulloa, Not. Amer., ent. 21. Humboldt, who analyzed the cement of the ancient structures at Cannar, says that it is a true mortar, formed of a mixture of pebbles and a clayey marl. (Vues des Cordilleres, p. 116.) Father Velasco is in raptures with an "almost imperceptible kind of cement" made of lime and a bituminous substance resembling glue, which incorporated with the stones so as to hold them firmly together like one solid mass, yet left nothing visible to the eye of the common observer. This glutinous composition, mixed with pebbles, made a sort of Macadamized road much used by the Incas, as hard and almost as smooth as marble. Hist. de Quito, tom. I. pp. 126-128.]