Against this solid society, as against some vast bare wall of brick, there surged age after age the nameless armies of the Nomads. They came out of the deserts where the nomadic life had been lived from the beginning and where it is still lived to-day. It is needless to dwell on the nature of that life; it was obvious enough and even easy enough to follow a herd or a flock which generally found its own grazing-ground and to live on the milk or meat it provided. Nor is there any reason to doubt that this habit of life could give almost every human thing except a home. Many such shepherds or herdsmen may have talked in the earliest times of all the truths and enigmas of the Book of Job; and of these were Abraham and his children, who have given to the modern world for an endless enigma the almost monomaniac monotheism of the Jews. But they were a wild people without comprehension of complex social organisation; and a spirit like the wind within them made them wage war on it again and again. The history of Babylonia is largely the history of its defence against the desert hordes; who came on at intervals of a century or two and generally retreated as they came. Some say that an admixture of nomad invasion built at Nineveh the arrogant kingdom of the Assyrians, who carved great monsters upon their temples, bearded bulls with wings like cherubim, and who sent forth many military conquerors who stamped the world as if with such colossal hooves. Assyria was an imperial interlude; but it was an interlude. The main story of all that land is the war between the wandering peoples and the state that was truly static. Presumably in prehistoric times, and certainly in historic times, those wanderers went westward to waste whatever they could find. The last time they came they found Babylon vanished; but that was in historic times and the name of their leader was Mahomet.