The transformation of the bedouin in Northern Arabia from small herders to militant rider-warriors in charge of large herds has been attributed to the development of dromedary riding technique and gear. The common origin of full bedouinization and the black tent, both of which have been traced back to Northern Arabia, suggests that they belong to the same stage of cultural evolution. The geographical extent of the Arabian group of tents is defined in the west by the Nile valley and in the south by the northern edge of the great sandy desert known as Rub al Khali. Tent awnings in the Arabian region are predominantly black goats' hair, although camels' hair is used occasionally. The Sba'a and the Ruwalla belong to a group of tribes known collectively as the Anaiza who control the steppelands of Northwestern Arabia. The Anaiza are a large loosely-knit group of tribes who occupy an area extending from North Arabia to Syria and Mesopotamia.