Asia Minor may be considered as the eastern emergence of the continental shelf supporting the European peninsula. Its salient physical features are a central plateau surrounded by a rim-like succession of ranges which are fringed in turn by a coastal strip of land. A gradual ascent from west to east can be observed. The western ranges have a mean altitude of about 2,000 feet above sea level. The plateau has an average height of 3,000 feet. The Armenian upland generally exceeds 4,000 feet. Access from the sea to the interior is impeded by the mountainous barrier reared as a natural bulwark. The gaps made by watercourses alone permit communication. As most of the rivers are not navigable, an important method of exploration is thus closed to adventurous roamers, whether native or foreign. This lack of fluvial communication has greatly hindered intercourse. Rivers have constituted the ancient ethnic boundaries between the inhabitants of the peninsula.[207] Communication between districts has been carried on mainly from harbor to harbor. Although the peninsula is in direct contact with three seas its mountainous rim prevents benign maritime influences from extending to its interior. Its climate may therefore be classed as extreme Mediterranean in type. All these combined factors annul to a large extent the effects of peninsular conditions. The region is not as salubrious as its elevation might imply. It is an area which has been occupied by communities of men actively engaged in human pursuits at various periods of history, and which has been subsequently abandoned to itself or rather to the working of causes in which man had no part. Gradual desiccation of the plateau is evinced by the presence of desert wastes coated with alkaline precipitates, by receding lakes and all the manifestations accompanying the decline of a hydrographic system. The salt lake occupying the central part of the plateau is in reality nothing but a vast marsh. Hydrographic changes are not confined merely to the interior of Asia Minor but exert their action on the coast itself. The bays of Tarsus and Ephesus are now much shallower than they were two thousand years ago.[208] The general result is to impair settlement. Reoccupation of the soil must often be preceded by sanitation and it is only within recent times that this important tool has been perfected by man so as to enable him to wield it effectively in the conquest of fresh sites of occupancy. Viewed therefore from its broadest aspect the problem of European control of Asia Minor resolves itself into one of renewed settlement. It is therefore pertinent to inquire how this condition coupled with regional influences has affected each of the six spheres.