INTRODUCTION TO SOCIOLOGY 669
by the trade winds and the equatorial current. London, as was very truly remarked by the illustrious J. Herschell, is not far from the geometric center of all the continental masses. There, too, all the lines of navigation of the world converge, just as formerly London was the natural half-way station between the Mediterranean and North Cape. Nothing proves better than the example of England that neither mountains nor water-courses, neither seas nor oceans, are natural frontiers, capable of serving as the basis for a theory, and still less for practice. They are, at the most, temporary obstacles, the material marks of social divi- sions in periods of history which are still primitive. The whole course of evolution, on the contrary, has resulted in making the island which we have made the type of the most complete isola- tion, in spite of its frontiers so clearly denned by the sea, in reality the geographical territory, the best adapted to the most complete social life. In this connection the evolution of Japan, that Eng- land of the Far East, has the same significance.
SECTION IX. THE EVOLUTION OF FRONTIERS TO THE END OF THE MIDDLE AGES, AND TO THE DISCOVERY OF THE NEW WORLD, AND THE PASSAGE AROUND THE CAPE OF GOOD HOPE
The Middle Ages were characterized, from the point of view of frontiers, by a continual displacement ; states were formed and broken down again without regard to geographical or ethnic con- ditions. In 711, Spain was wrested from the Visigoths by the Arabs; the peninsula became a province of the empire of the caliph of Damascus ! From the year 756 it became an emirate or separate caliphate, that of Cordova, until the year 1031. This caliphate included at first Septimania beyond the Pyrenees, but it was lost in the year 759. The caliphate never succeeded in extending itself into the Asturian and Cantabrian mountain region in the northwest. There an independent Christian king- dom was established by the most energetic mountaineers and refugees. Successively Galicia and the whole coast as far as the Douro were annexed by the Mussulmans and then the whole basin of the Douro. The two powers were for the moment delimited, but not separated, by the ranges of the Sierra de Credos and the
