Switzerland has no natural frontiers. The mountains and valleys of the Alps continue to the east and west into what is now Austria and France as they do on the southern slopes into what is now Italy. That the Bregaglia and the valley of Poschiavo are Swiss, while the Valtellina or the county of Bormio are Italian, can only be understood historically. Every Swiss frontier represents an historic act or set of events. Vorarlberg is Austrian because the Great Powers in 1919 refused to accept a plebiscite of its people for union with Switzerland. Geneva's borders on Lac Léman were settled by the Vienna Congress. Canton Ticino was conquered by Uri and later by other Swiss cantons. Constance, the ‘natural’ capital of the Thurgau, is German, partly because the Swiss Diet lacked the nerve in 1510 to accept another city-state into the Federation for fear of upsetting the urban-rural balance. Canton Schaffhausen contains one parcel of 41 hectares in its midst which is, in fact, German territory, and has three substantial enclaves, which cannot be reached without passing through German territory. Nor is the picture more coherent within Switzerland. Boundaries between cantons wander irregularly and unexpectedly over the landscape. Bits and pieces of Canton Solothurn lie embedded in Canton Bern, two of which, Kleinlützel and Mariastein, have borders with France as well.