There are several groups of pyramids, large and small at Gizeh and elsewhere, almost all of which belong to the Old Empire. The three great pyramids of Gizeh are among the earliest. They were built by three kings of the Fourth Dynisty, Cheops (Chufu), Chephren (Chafre), and Mycerinus (Menkere) They are gigantic sepulchral monuments in which the mummies of the kings who built them were deposited. The pyramid of Cheops (Fig. 1, at the right), the largest of all, was originally 481 feet 4 inches in height, and was thus doubtless the loftiest structure ever reared in pre- Christian times. The side of the square base measured 755 feet 8 inches. The pyramidal mass consists in the main of blocks of limestone, and the exterior was originally cased with fine limestone, so that the surfaces were perfectly smooth. At present the casing is gone, and instead of a sharp point at the top there is a platform about thirty feet square. In the heart of the mass was the granite chamber where the king's mummy was laid. It was reached by an ingenious system of passages, strongly barricaded. Yet all these precautions were ineffectual to save King Cheops from the hand of the spoiler. Chephren's pyramid (Fig. 1, at the left) is not much smaller than that of Cheops, its present height being about 450 feet, while the height of the third of this group, that of Mycerinus, is about 210 feet. No wonder that the pyramids came to be reckoned among the seven wonders of the world. While kings erected pyramids to serve as their tombs, officials of high rank were buried in, or rather under, structures of a different type, now commonly known under the Arabic name of mastabas. The mastaba may be described as a block of masonry of limestone or sun-dried brick, oblong in plan, with the sides built "battering," i.e., sloping inward, and with a flat top. It had no architectural merits to speak of, and therefore need not detain us. It is worth remarking, however, that some of these mastabas contain genuine arches, formed of unbaked bricks. The knowledge and use of the arch in Egypt go back then to at least the period of the Old Empire. But the chief interest of the mastabas lies in the fact that they have preserved to us most of what we possess of early Egyptian sculpture. For in a small, inaccessible chamber (serdab) reserved in the mass of masonry were placed one or more portrait statues of the owner, and often of his wife and other members of his household, while the walls of another and larger chamber, which served as a chapel for the celebration of funeral rites, were often covered with painted bas- reliefs, representing scenes from the owner's life or whatever in the way of funeral offering and human activity could minister to his happiness.