There is no rainfall in the valley and little in the delta, so whatever moisture Egypt receives must come from the Nile. The entire valley is not of equal elevation but becomes higher as it spreads out on either side, and so a vast system of irrigation must be maintained to make good crops possible. Large sums have been expended in the construction of dams, embankments and canals to contain the water after the river recedes, allowing the amount thus retained to be drawn off as it is needed. From canals it is drawn off into trenches for still higher land, and artificial means of various kinds have always been employed to lift the water from one level to another. It is estimated that tens of thousands of men and boys are constantly engaged in this elevation of water from one level to another, in order that farms throughout the valley may receive the necessary moisture and fertility. As rapidly as one crop is harvested, the soil is made ready for another, so that as many as five crops are frequently harvested in a year on a given acreage. INFLUENCE OF TOPOGRAPHY. With a sea on the north, mountains on the east, cataracts to the south and a desert on the west, what would be the natural effect upon the inhabitants of physical conditions such as these prevailing in the land of Egypt? They determined that the Egyptians would be left to develop their civilization unmolested for the most part by outside influences. Such physical features account for the fact that for hundreds of years that was a land, not of war, but of peace. Think for a moment what natural boundaries have meant to nations of Europe. England's isolation has been largely due to her stormy channel, while the independence of the Swiss is accounted for by their inaccessible mountain home. Austria, on the other hand, has known the disastrous effects of repeated invasions, while Poland has lost her identity and has been appropriated by her neighbors because of unfortunate situation and the lack of natural defenses.