Until such is hit upon we must remain in ignorance of the real mode of sepulture in those days, and of the purpose of many of the arrangements in these mysterious buildings. The portcullises which invariably close the entrances of the sepulchral chamber in the pyramids are among the most curious and ingenious of the arrangements of these buildings. Generally they consist of great cubical masses of granite, measuring 8 or 10 ft. each way, and consequently weighing 50 or 60 tons, and even more. These were fitted into chambers prepared during the construction of the building, but raised into the upper parts, and, being lowered after the body was deposited, closed the entrance so effectually that in some instances it has been found necessary either to break them in pieces, or to cut a passage round them, to gain admission to the chambers. They generally slide in grooves in the wall, to which they fit exactly, and altogether show a degree of ingenuity and forethought very remarkable, considering the early age at which they were executed. In the Second Pyramid one chamber has been discovered partly above-ground, partly cut in the rock. In the Third the chambers are numerous, all excavated in the rock; and from the tunnels that have been driven by explorers through the superstructures of these two, it is very doubtful whether anything is to be found above-ground.[36] All the old pyramids do not follow the simple outline of those at Gizeh. That at Dahshur, for instance, rises to half the height, with a slope of 54° to the horizon, but is finished at the angle of 45°, giving it a very exceptional appearance. The pyramids of Sakkara and Medum are of the class known as mastaba pyramids, the term mastaba (Arabic for bench) being given to the sloping-sided tombs of about 76° angle and from 10 to 20 ft. high. No. 9. [Illustration: No. 10. Pyramid of Sakkara. (From Colonel Vyse’s work.) Scale 100 ft to 1 in.] The annexed plan and section of Sakkara (Woodcut Nos. 9 and 10), both to the scale of 100 ft. to 1 in., show the peculiar nature of their construction, which seems to have been cumulative; that is to say, they have been enlarged in successive periods, the original casing of the earlier portions having been traced. Mr. Petrie says: “Both of these structures have been several times finished, each time with a close-jointed polished casing of the finest white limestone, and then, after each completion, it has been again enlarged by another coat of rough masonry and another line casing outside.”