The nature of the soil does not allow of deep foundations.  It consists of a thin bed of made earth, which, except in large towns, never reaches any degree of thickness; below this comes a very dense humus, permeated by slender veins of sand; and below this again—­at the level of infiltration—­ comes a bed of mud, more or less soft, according to the season.  The native builders of the present day are content to remove only the made earth, and lay their foundations on the primeval soil; or, if that lies too deep, they stop at a yard or so below the surface.  The old Egyptians did likewise; and I have never seen any ancient house of which the foundations were more than four feet deep.  Even this is exceptional, the depth in most cases being not more than two feet.  They very often did not trouble themselves to cut trenches at all; they merely levelled the space intended to be covered, and, having probably watered it to settle the soil, they at once laid the bricks upon the surface.  When the house was finished, the scraps of mortar, the broken bricks, and all the accumulated refuse of the work, made a bed of eight inches or a foot in depth, and the base of the wall thus buried served instead of a foundation.  When the new house rose on the ruins of an older one decayed by time or ruined by accident, the builders did not even take the trouble to raze the old walls to the ground.  Levelling the surface of the ruins, they-built upon them at a level a few feet higher than before:  thus each town stands upon one or several artificial mounds, the tops of which may occasionally rise to a height of from sixty to eighty feet above the surrounding country.  The Greek historians attributed these artificial mounds to the wisdom of the kings, and especially to Sesostris, who, as they supposed, wished to raise the towns above the inundation.  Some modern writers have even described the process, which they explain thus:—­A cellular framework of brick walls, like a huge chess-board, formed the substructure, the cells being next filled in with earth, and the houses built upon this immense platform (Note 5).

[Illustration:  Fig. 2.—­Ancient house with vaulted floors, against the northern wall of the great temple of Medinet Habu]

[Illustration:  Fig. 3.—­Plan of three-quarters of the town of Hat-Hotep-Usertesen (Kahun), built for the accommodation of the officials and workmen employed in connection with the pyramid of Usertesen II. at Illahun.  The workmen’s quarters are principally on the west, and separated from the eastern part of the town by a thick wall.  At the south-west corner, outside the town, stood the pyramid temple, and in front of it the porter’s lodge.  Reproduced from Plate XIV. of Illahun, Kahun, and Gurob, W.M.F.  Petrie.]