The sands of the deserts would, no doubt, have guarded the houses of Memphis and Thebes as effectually as the cinders of Vesuvius did those of the little Roman town, if they had had but the same chance. We know how thoroughly they protected the dwellings of the dead upon the plateau of Gizeh, but the homes of the living were built close to the river and not upon the borders of the desert, and we can neither hope to find dead cities under the Egyptian sands, nor such indications of their domestic architecture as those which may sometimes be gleaned in mountainous countries. Their situation upon the banks of the river, or not far from it, made it necessary for Egyptian cities to be placed upon artificial mounds or embankments, which should raise them above the inundation. Those modern villages, which are not built upon the slopes of the mountain, are protected in the same fashion. The tradition has survived of the great works undertaken during the period of national prosperity in order to provide this elevated bed for the chief cities of the country. According to Herodotus and Diodorus, Sesostris and Sabaco, that is to say the great Theban princes and the Ethiopian conquerors, were both occupied with this work of raising the level of the towns.[17] Some idea of the way in which these works were carried out has been gained by excavations upon the sites of a few cities. When a new district was to be added to a city the ground was prepared by building with crude brick a number of long and thick walls parallel to one another; then cross walls at right angles with the first, chessboard fashion. The square pits thus constructed were filled with earth, broken stone, or anything else within reach. The foundations of the future city or district were laid upon the mass thus obtained, and profited by the operation both in health and amenity. The cities of Memphis and Thebes both seem to have been built in this manner.[18] [17] HERODOTUS, ii. 137; DIODORUS, i. 57. [18] ÉDOUARD MARIETTE, _Traité pratique et raisonné de la Construction en Égypte_, p. 139. As a rule this is all that we learn by excavating on these ancient sites. The materials of the houses themselves have either fallen into dust, or, in a country which has been thickly populated since long before the commencement of history, have been used over and over again in other works. The inevitable destruction has been rendered more rapid and complete by the fellah's habit of opening up any mounds which he has reason to believe ancient, for the sake of the fertilizing properties they possess.