Barrier boundary of the Mediterranean basin and its northern breaches as factors in history

The Mediterranean occupies the subsidence areas in the broad belt of young, folded mountains which cross Southern Europe and the neighbouring parts of Africa and Asia. Moreover, it lies on the northern margin of the trade- wind tract. These two features of its geographical location are of immense import. They have given to the Mediterranean Basin the isolating boundaries of mountains and deserts. They have made it in a peculiar sense an enclosed sea. It is enclosed, not only by the land, but by barrier forms of the land. Rarely are the barriers single, moreover. Range succeeds range to a snow-capped climax of the land : beyond mountain system or precipitous escarpment lies semi-arid waste, far stretching desert, or rugged plateau. (Summary by Ellen Churchill Semple)