Nevertheless, while Egypt suffered many invasions, she maintained with considerable constancy the ancient racial traits, and had a continuity of development through the passing centuries which retained many of the primitive characteristics. The valley of the Euphrates was kept fertile by the flow of the great rivers, the Tigris and Euphrates, which, having a large watershed in the mountains, brought floods down through the valleys bearing the silt which made the land fertile. But in both countries at an early period the population encroached upon the natural supply of food, and methods of irrigation were introduced to increase the food supply. The attempts to build palaces, monuments, and tombs were characteristic of both peoples. On account of the dryness of the climate, these great monuments have been preserved with a freshness through thousands of years. In the valley of the Euphrates many of the cities that were reduced to ruin were covered with the drifting sands and floods until they are buried beneath the surface. In sculpture, painting, and in art, as well as in permanency of her mighty pyramids, sphinxes, and tombs, Egypt stands far ahead of Babylonia. The difference is mainly expressed in action, for in Egypt there is an expression of calm, solemnity, and peace in the largest portions of the architectural works, while in Babylonia there is less skill and more action. The evidences of the type of civilization are similar in one respect, namely, that during the thousand years of development the great monuments were left to show the grandeur of kings, monarchs, and priests, built by thousands of slaves suffering from the neglect of their superiors through ages of toil. Undoubtedly, this failure to recognize the rights of suffering humanity gradually brought destruction upon these great nations. If the strength of a great nation was spent in building up the mighty representations of the glory and power of kings {164} to the neglect of the improvement of the race as a whole, it could mean nothing else but final destruction.