Climatic changes covering thousands of years, which may be summarized in popular language as the recession of the last Ice Age, had by about 6000 B.C. reduced large tracts of the Middle East to the virtually rainless and desert conditions which still obtain in the Sahara, lying athwart Africa with a depth of 1000 miles from north to south, and its extension, the Arabian Desert. To the north of this sterile belt, the mountain-ranges of Syria, Anatolia, and Persia receive an adequate winter rainfall from the Mediterranean; and this relatively well-watered region is flanked to west and east by the basins of two great river-systems, the Nile and the Euphrates-Tigris, to form a Fertile Crescent which was in all probability the home of the original Agricultural Civilization to which reference. The state of society in the Middle East in A.D. 600 was still the direct outcome of the expansion and development of this Agricultural Civilization. Agriculture had naturally not been possible in the desert regions, except in small cases isolated from one another, where water could be tapped by wells but in the marginal lands one of the arts of this civilization.