The enormous rectangular mass which the Arabs call _Mastabat el Faraûn_, "the seat of Pharaoh" (fig. 141), stands beside the pyramid of Pepi II. Some have thought it to be an unfinished pyramid, some a tomb surmounted by an obelisk; in reality it is a pyramid which was left unfinished by its builder, King Ati of the Sixth Dynasty. Recent excavations have, on the other hand, shown that the brick pyramids of Dahshûr probably belonged to the Twelfth Dynasty. The stone pyramids of that group, which may be older, furnish a curious variation from the usual type. One of these stone pyramids has the lower half inclined at 54° 41', while the upper part changes sharply to 42° 59'; it might be called a mastaba (Note 35) crowned by a gigantic attic. At Lisht, where the two pyramids now standing are of the same period (one of them was erected by Ûsertesen I.), the structure is again changed. The sloping passage ends in a vertical shaft, at the bottom of which open chambers now filled by the infiltration of the Nile. The pyramids of Illahûn and Hawara, which contained the remains of Ûsertesen II. and Amenemhat III., are of the same type as those at Lisht. Their rooms are now filled with water. The pyramid of Medûm is empty, having been violated before the Ramesside age. It consists of three square towers (Note 36) with sides slightly sloping, placed in retreating stages one over the other (fig. 142). The entrance is on the north, at about 53 feet above the sand. After 60 feet, the passage goes into the rock; at 174 feet it runs level; at 40 feet farther it stops, and turns perpendicularly towards the surface, opening in the floor of a vault twenty-one feet higher (fig. 143). A set of beams and ropes still in place above the opening show that the spoilers drew the sarcophagus out of the chamber in ancient times. Its small chapel, built against the eastern slope of the pyramid, with courtyard containing a low flat altar between two standing stelae nearly 14 feet high, was found intact. The walls of the chapel were uninscribed, and bare; but the _graffiti_ found there prove that the place was much visited during the times of the Eighteenth Dynasty by scribes, who recorded their admiration of the beauty of the monument, and believed that King Sneferû had raised it for himself and for his queen Meresankhû. [Illustration: Fig. 143.--Section of passage and vault in pyramid of Medûm.]