These two pyramids are the only two genuine stepped pyramids, all the others having had an uniform casing on one slope (excepting Dahshur, as above mentioned). The Pyramid of Sakkara is the only pyramid that does not face exactly north and south. It is nearly of the same general dimensions as the Third Pyramid, that of Mycerinus; but its outline, the disposition of its chambers, and the hieroglyphics found in its interior, all would seem to point it out as an imitation of the older form of mausolea by some king of a far more modern date. MEDUM. Mr. Flinders Petrie’s discoveries in 1891 determined the age and the construction of the Pyramid of Medum,[37] erected by Seneferu, a king of the third dynasty, being therefore the oldest pyramid known. Its construction resembles that of the small pyramid of Rikheh and the oblong step pyramid of Sakkara, that is to say, it is a cumulative mastaba, the primal mastaba being about 150 ft. square, and from 37 to 45 ft. high. The outer coatings added were seven in number, and the original mass was carried up and heightened as the circuit was increased, and lastly an outer casing covered over all the steps which had resulted during the construction. The average length of the base was 473 ft. 6 in., the total height being 301 ft. 7 in. According to Mr. Petrie, the Pyramid of Medum, as those of Sakkara and Rikheh, were of a transitional form, in which the original mastaba had been greatly enlarged and subsequently covered over with a casing of pyramidal outline. “That type once arrived at, there was no need for subsequent kings to retain the mastaba form internally, and Khufu and his successors laid out their pyramids of full size at first and built them up at an angle of 51°, and not at 75°, that which is found in the ordinary mastabas.” Mr. Petrie also discovered the temple of the pyramid in the middle of its east side, and almost uninjured. It consisted of a passage entered at the south end of east front, then a small chamber and a courtyard adjoining the side of the pyramid, containing two steles and one altar between them. In the sepulchral pit of Rahotep, near the pyramid, Mr. Petrie found two arches thrown across a passage to relieve the thrust of the overlapping sides, which carries the use of that feature back to the 4th dynasty. TOMBS.