§ 9. _The Illumination of the Temples._ We have described the way in which the Egyptian architects treated doors and windows from an artistic point of view; we have yet to show the method which they adopted for allowing sufficient light to penetrate into their temples, that is, into those buildings, which, being closely shut against the laity, could not be illuminated from windows in their side walls. Palaces and private houses could have their windows as large and as numerous as they chose, but the temple could only be lighted from the roof, or at least from parts contiguous to the roof. [Illustration: FIG. 155.--Attic of the Great Hall at Karnak. Restored by Ch. Chipiez.] [Illustration: FIG. 156.--_Claustra_ of the Hypostyle Hall, Karnak. _Description_, iii. 23.] The hypostyle hall at Karnak, with its lofty walls and close ranges of columns, would have been in almost complete darkness had it been left to depend for light upon its doors alone. But the difference of height between the central aisle and those to the right and left of it, was taken advantage of to introduce the light required for the proper display of its magnificent decorations. The wall which filled up the space between the lower and upper sections of roof, forming something almost identical with the clerestory of a Gothic cathedral, was constructed of upright sandstone slabs, about sixteen feet high, which were pierced with numerous perpendicular slits. Stone gratings, or _claustra_ as the Romans would have called them, were thus formed, through which the sunlight could stream into the interior. The slits were about ten inches wide and six feet high. The illustration on page 163 shows how the slabs were arranged and explains, moreover, the general disposition of the roof. Fig. 156 gives the _claustra_ in detail, in elevation, in plan, and in perspective. The hypostyle halls are nearly always lighted upon the same principle. The chief differences are found in the sizes of the openings. At the Temple of Khons, where the space to be lighted was not nearly so large, the slabs of the _claustra_ were much smaller and the openings narrower (Fig. 157). In one of the inner halls at Karnak a different system has been used. The light penetrates through horizontal openings in the entablature, between the architrave and the cornice, divided one from another by cubes of stone (Fig. 158). In the inside the architrave was bevelled on its upper edge, so as to allow the light to penetrate into the interior at a better angle than it would otherwise have done. [Illustration: FIG. 157.--_Claustra_ in the Hypostyle Hall of the Temple of Khons. Compiled from the elevations in the _Description_, iii. 28.]