[Sidenote:  Economic and political importance of lakes.]

A river that spreads out into the indeterminate earthform of a marsh is an effective barrier; but one that gathers waters into a natural basin and forms a lake retains the uniting power of a navigable stream and also, by the extension of its area and elimination of its current, approaches the nature of an enclosed sea.  Mountain rivers, characterized by small volume and turbulent flow, first become navigable when they check their impetuosity and gather their store of water in some lake basin.  The whole course of the upper Rhone, from its glacier source on the slope of Mount Furca to its confluence with the Saone at Lyon, is unfit for navigation, except where it lingers in Lake Geneva.  The same thing is true of the Reuss in Lake Lucerne, the upper Rhine in Lake Constance, the Aare in Thun and Brienze, and the Linth in Lake Zurich.  Hence such torrent-fed lakes assume economic and political importance in mountainous regions, owing to the paucity of navigable waterways.  The lakes of Alpine Switzerland and Italy and of Highland Scotland form so many centers of intercourse and exchange.  Even such small bodies of water as the Alpine lakes have therefore become goals of expansion, so that we find the shores of Geneva, Maggiore, Lugano, and Garda, each shared by two countries.  Switzerland, the Austrian Tyrol, and the three German states of Baden, Wurtemberg and Bavaria, have all managed to secure a frontage upon Lake Constance.  Lake Titicaca, lying 12,661 feet (3854 meters) above sea level but affording a navigable course 136 miles (220 kilometers) long, is an important waterway for Peru and Bolivia.  In the central Sudan, where aridity reduces the volume of all streams, even the variable and indeterminate Lake Chad has been an eagerly sought objective for expanding boundaries.  Twenty years ago it was divided among the native states of Bornu, Bagirmi and Kanem; today it is shared by British Nigeria, French Sudan, and German Kamerun.  The erratic northern extension of the German boundary betrays the effort to reach this goal.

[Sidenote:  Lakes as nuclei of states.]

The uniting power of lakes manifests itself in the tendency of such basins to become the nuclei of states.  Attractive to settlement in primitive times, because of the protected frontier they afford—­a motive finding its most emphatic expression in the pile villages of the early lake-dwellers—­later because of the fertility of their bordering soil and the opportunity for friendly intercourse, they gradually unite their shores in a mesh of reciprocal relations, which finds its ultimate expression in political union.  It is a significant fact that the Swiss Confederation originated in the four forest cantons of Lucerne, Schwyz, Uri and Unterwalden, which are linked together by the jagged basin of Lake Lucerne or the Lake of the Four Forest Cantons, as the Swiss significantly call it, but are otherwise divided by mountain barriers.