The most southerly of them is Belfort,[133] which you will find standing on a plain within fifteen miles of the Swiss border. This plain is called by soldiers "the Gap of Belfort," and it is the only real break in the hill frontier that covers France all the way from the Mediterranean to Flanders. You can see at a glance that if the Gap were not strongly fortified an army could easily march into France from the direction of the Rhine. To block this easy road the French have constructed the very strong ring-fortress of Belfort. It was besieged during the Franco-German War, and yielded on February 13, 1871; but its defenders made such a gallant resistance that they were allowed to march out with what are called the honours of war--that is, with their drums beating, their flags flying, and their arms in their hands. To commemorate the siege, a huge lion has been carved on the face of the precipice below the castle by the sculptor of the statue of Liberty in New York harbour.[134] One wonders why the Germans did not take over Belfort after their conquest. Had they done so, they would have provided themselves with an ever-open door into France. Rising steeply from the Gap, and running north-north-east for 150 miles is the highland region known as the Vosges Mountains. Since 1871 the frontier between France and Germany has run along the crest of these mountains for about fifty miles. The Vosges consist chiefly of granite rocks, and everywhere there are signs that they were once covered with glaciers. We still see the old moraines, consisting of the heaps of rock and soil that were left behind when the glaciers melted, and the lakes that were scooped out by the great ice fields that slowly crept over the mountains in bygone ages. We also see the rounded summits which the French call _ballons_. The highest of these _ballons_ are over 4,000 feet in elevation, and are to be found about twenty miles north of Belfort. The Vosges fall steeply to the Alsatian plain, but descend gradually to the west. No single railway crosses them between the Gap of Belfort and the gap which you see to the north of Strassburg, but many carriage roads traverse the passes. The whole region is very picturesque; the lakes are surrounded by forests of pine, beech, and maple; there are many green meadows, which provide pasturage for large herds of cattle; numerous ruined castles stand on the spurs, and the lower slopes are studded with vineyards.