the arabian peninsula has the shape of an irregular rectangle. on the north it is bounded by palestine and the syrian desert; on the east by the kingdom of al hirah, the euphrates and tigris and the persian gulf; on the south by the indian ocean and the gulf of `adan; and to the west by the red sea. the natural isolation of the peninsula combined with its size to protect it against invasion. the peninsula is over a thousand kilometers long and as wide. moreover, this vast expanse is utterly uncultivable. it does not have a single river nor a dependable rainy season around which any agriculture could be organized. with the exception of fertile and rainy yaman in the southwest, the peninsula consists of plateaus, valleys and deserts devoid of vegetation and an atmosphere so inclement that no civilization could prosper therein. the arabian peninsula allows only desert life; and desert life demands continuous movement, adoption of the camel as means of transportation, and the pursuit of thin pasture which is no sooner discovered than it is exhausted and another movement becomes imperative. these well sought-after pastures grow around springs whose waters have collected from rainfall on the surrounding rocky terrain, allowing a scarce vegetation to grow in the immediate vicinity.