Though explicit pronouncements are difficult to find, the historical literature on the Middle East seems to be based on the assumption that the large desert areas contain societies and economic systems which are for the most part autonomous, but which occasionally impinge--sometimes with catastrophic results--on the lusher agricultural and urbanized areas. The deserts are designated by terms equivalent to "wilderness" and "area of insolence"; they are represented as areas controlled by nomads, who are by definition opposed to the settled life of cities and agricultural villages. The cities with their agricultural hinterland represent order and security, while the nomads stand for chaos. Finally, from time to time, the nomads erupt out of the desert and overrun the good land of the true believers.