There is the same variety in the position of the mummy chamber. Sometimes this is within the sides of the pyramid itself, as in that of Cheops; sometimes, after the example of the mastaba, it is cut out of the living rock upon which the pyramid stands. This arrangement is to be found, for instance, in the pyramid of Mycerinus, where the roof of the mummy chamber is about 33 feet below the lowest course of the pyramid itself. So too in the Stepped Pyramid, where the whole complicated system of corridors and cells, which distinguishes that edifice, is cut in the rock, so that the building itself is absolutely solid. Most of the pyramids have no more than one or two entrances, giving access to narrow galleries, sometimes ascending, sometimes descending, which lead to one or two chambers of very small dimensions when compared to the enormous mass which rises above and around them (Fig. 132). In the subterranean part of the Stepped Pyramid the proportion of voids to solids is far less insignificant. This pyramid, which is not nearly so carefully oriented as the others, has four entrances and a series of internal passages, horizontal galleries, staircases and cells, which make it little else than a subterranean labyrinth. It is singular also in having, upon its central axis and at the point upon which, at various heights, all its galleries converge, a sort of large well, a chamber about twenty feet square and eighty feet high, in the pavement of which a huge block of granite cut into the shape of a cork or plug was so placed as to open at will[191] and leave a free passage for the descent into a second chamber, the purpose of which is more than obscure, as it is too small even to have contained a sarcophagus.[192] The end of the long passage which leads to the thirty chambers which have been counted beneath this pyramid has been found in the neighbouring sands (Fig. 134). [191] The weight of this stopper is about four tons, and it has long been a puzzle to egyptologists how it, and others like it, could be raised and lowered. M. Perrot's words must not, therefore, be taken too literally.--ED. [192] ARTHUR RHONÉ, _L'Égypte à petites Journées_, p. 259. [Illustration: FIG. 131.--The pyramid of Illahoun, horizontal section in perspective; from the plan of Perring.] Another point of difference: most of the pyramids are built round a core of living rock, which is embraced by the lower courses of their masonry. But the pyramid of Mycerinus is just the reverse of this. It is built over a hollow in the rock which is filled up with masonry. The inequalities of the surface were usually taken advantage of so as to economize material, and make a greater show with less labour. Mycerinus, however, did not fear to increase his task by rearing his pyramid over a depression in the plateau. [Illustration: FIG. 132.--Section of the pyramid of Cheops; from Perring.]