[Illustration: FIG. 150.--Method of closing a gallery by a stone portcullis; from the southern pyramid of Dashour. Drawn in perspective from the plans and elevations of Perring.] [Illustration: FIG. 151.--Portcullis closed.] Another ingenious arrangement which demands our notice is that of those discharging chambers to which we have already alluded. These chambers were explored, not without trouble, by Colonel Howard Vyse and J. L. Perring, who at once comprehended their use. The roof of the sarcophagus-chamber consists of nine slabs of fine red granite, like those which form the walls of the same chamber. They are 18 feet 9 inches long and their ends rest upon the side walls of the chamber. In spite of their thickness and of the hard nature of the rock of which they are composed, it was feared that they might give way under the enormous weight of the masonry above, for the floor of the chamber is still nearly 340 feet below the actual apex of the pyramid. This danger was met in the fashion figured above. [Illustration: FIG. 152.--Transverse section, in perspective, through the sarcophagus-chamber and the discharging chambers; from the elevation of Perring.] As the structure grew above the roof of the mummy-chamber, five small chambers were left, one above the other, to a total height of 56 feet, which would relieve the flat ceiling of the mummy-chamber of the weight to be placed above it. The first four of these chambers were of similar shape and had flat roofs, but the roof of the fifth was formed of sloping slabs, meeting in a ridge, and giving the chamber a triangular section (see Fig. 152). Thanks to this succession of voids immediately over the main chamber, and to the pointed arch which surmounts them, the vertical pressure of the superstructure is discharged from the chamber itself and distributed over the lateral parts of the pyramid. These precautions have been quite effectual. Not a stone has been stirred either by the inward thrust or by the crushing of their substance; not a block is out of place but those which have been disturbed by the violence of man; and, moreover, the whole structure is so well bonded and so well balanced that even his violent attacks have led neither to disruption nor settlement in the apartment of Cheops or in the galleries which lead to it.[204] [204] The discovery of these chambers was interesting from another point of view. The name of Choufou was found continually repeated upon the blocks of which they are formed. It was written in red ochre, and, in places, it was upside down, thus proving that it must have been written before the stones were put in place. It cannot therefore have been traced after the tradition which assigned the pyramid to Cheops, that is, to Khoufou, arose; and so it affords conclusive corroboration of the statements of Herodotus. [Illustration: FIG. 153.--Longitudinal section through the lower chambers; perspective after Perring.]