For the people of the desert were as little static as the people of the hills. The economic life of the desert was based on the supply of camels, which were best bred on the rigorous upland pastures with their strong nutritive thorns. By this industry the Bedouins lived; and it in turn moulded their life, apportioned the tribal areas, and kept the clans revolving through their rote of spring, summer and winter pasturages, as the herds cropped the scanty growths of each in turn. The camel markets in Syria, Mesopotamia, and Egypt determined the population which the deserts could support, and regulated strictly their standard of living. So the desert likewise overpeopled itself upon occasion; and then there were heavings and thrustings of the crowded tribes as they elbowed themselves by natural courses towards the light. They might not go south towards the inhospitable sand or sea. They could not turn west; for there the steep hills of Hejaz were thickly lined by mountain peoples taking full advantage of their defensiveness. Sometimes they went towards the central oases of Aridh and Kasim, and, if the tribes looking for new homes were strong and vigorous, might succeed in occupying parts of them. If, however, the desert had not this strength, its peoples were pushed gradually north, up between Medina of the Hejaz and Kasim of Nejd, till they found themselves at the fork of two roads. They could strike eastward, by Wadi Rumh or Jebel Shammar, to follow eventually the Batn to Shamiya, where they would become riverine Arabs of the Lower Euphrates; or they could climb, by slow degrees, the ladder of western oases—Henakiya, Kheibar, Teima, Jauf, and the Sirhan—till fate saw them nearing Jebel Druse, in Syria, or watering their herds about Tadmor of the northern desert, on their way to Aleppo or Assyria.
Nor then did the pressure cease: the inexorable trend northward continued. The tribes found themselves driven to the very edge of cultivation in Syria or Mesopotamia. Opportunity and their bellies persuaded them of the advantages of possessing goats, and then of possessing sheep; and lastly they began to sow, if only a little barley for their animals. They were now no longer Bedouin, and began to suffer