The extent and magnificence of Assyrian building must have demanded an immense supply of such manual labour for the purpose of brickmaking. All the mighty works of ancient Egypt, Assyria, and Babylon were literally "the work of men's hands." In Mesopotamia was captured labour especially necessary. Stone was indeed available at Nineveh, but the barrenness of the soil which stretches flatly from the rugged hills of Kurdistan across Mesopotamia rendered the country unproductive unless enormous works of irrigation were undertaken for the distribution of water. Mesopotamia is a country of immense possibilities, but the wealth of it is only for those who can distribute the waters of its great rivers over the productive soil. The yearly inundations of the Euphrates and Tigris are but sufficient for the needs of a narrow strip of land on either side the rivers, and the crops of the country undeveloped by canals can only support a scattered and scanty population. Towards the south there is another difficulty. The flat soil becomes water-logged and marshy and runs to waste for want of drainage. There is no stone for building purposes near Babylon. Approaching Babylon over the windy wastes of scrub-powdered plain there is nothing to be seen in the shape of a hill. Long, low, flat-topped mounds stretch athwart the horizon and resolve themselves on nearer approach into deeply scarred and weather-worn accretions of debris, or else they are banks of ancient waterways winding through the steppe, the last remnants of a stupendous system of irrigation. Then there breaks into view the solitary erection which stands in the open plain overlooking a wide vista of marsh and swamp to the west, which represents the ruins called Birs Nimrud, the Ziggurat or temple which, in successive tiers devoted to the powers of heaven, supported the shrine of Mercury. It is by far the most conspicuous object in the Babylonian landscape; huge, dilapidated, and unshapely, it mounts guard over a silent, stagnant, swampy plain.