50 feet in height. The dam, which is 143 feet in thickness, consists of
three layers of material; at the bottom, a bed of clay and rubble; next, a
piled mass of limestone blocks (A); lastly, a wall of cut stone built in
retreating stages, like an enormous flight of steps (B). Thirty-two of the
original thirty-five stages are yet _in situ_, and about one-fourth part of
the dam remains piled up against the sides of the ravine to right and left;
but the middle part has been swept away by the force of the torrent (fig.
48). A similar dike transformed the end of Wady Genneh into a little lake
which supplied the Sinaitic miners with water.

Most of the localities from which the Egyptians derived their metals and
choicest materials in hard stone, were difficult of access, and would have
been useless had roads not been made, and works of this kind carried out,
so as to make life somewhat less insupportable there.

[Illustration: Fig. 48.--Section of dike at Wady Gerraweh.]

In order to reach the diorite and grey granite quarries of the Hammamat
Valley, the Pharaohs caused a series of rock-cut cisterns to be constructed
along the line of route. Some few insignificant springs, skilfully
conducted into these reservoirs, made it possible to plant workmen's
villages in the neighbourhood of the quarries, and also near the emerald
mines on the borders of the Red Sea. Hundreds of hired labourers, slaves,
and condemned criminals here led a wretched existence under the rule of
some eight or ten overseers, and the brutal surveillance of a company of
Libyan or negro mercenary troops. The least political disturbance in Egypt,
an unsuccessful campaign, or any untoward incident of a troubled reign,
sufficed to break up the precarious stability of these remote
establishments. The Bedawîn at once attacked the colony; the workmen
deserted; the guards, weary of exile, hastened back to the valley of the