The origin of these peoples was an academic question; but for the understanding of their revolt their present social and political differences were important, and could only be grasped by looking at their geography. This continent of theirs fell into certain great regions, whose gross physical diversities imposed varying habits on the dwellers in them. On the west the parallelogram was framed, from Alexandretta to Aden, by a mountain belt, called (in the north) Syria, and thence progressively southward called Palestine, Midian, Hejaz, and lastly Yemen. It had an average height of perhaps three thousand feet, with peaks of ten to twelve thousand feet. It faced west, was well watered with rain and cloud from the sea, and in general was fully peopled.