In 1914 the Dolomites were part of the Austro-Hungarian Empire, which was part of the Central Powers during the First World War. In 1915, Italy joined the alliance of Britain, France, and Russia and declared war on the Central Powers. Austria's troops were heavily committed in Russia and it immediately withdrew to a defensive line which ran through the Dolomites. Until the end of 1918 the Austrians (supported by troops from Southern Germany) and the Italians fought a ferocious war in the mountains of the Dolomites; not only against each other but also against the hostile conditions. Both sides tried to gain control of the peaks to site observation posts and field guns. To help troops move about at high altitude in very difficult conditions, permanent lines were fixed to rock faces and ladders were installed so that troops could ascend steep faces. They also tried to create and control tunnels below the peaks to attack from there (see Mines on the Italian Front). Trenches, dugouts and other relics of the First World War can be found alongside many via ferratas. There is an extensive open-air museum on 5 Torri, and around Lagazuoi, where very heavy fighting took place. This wartime network of via ferratas has been restored, although not until well after the Second World War: steel cables have replaced ropes, and iron ladders and metal rungs anchored into the rock have taken the place of the flimsy wooden structures used by the troops. These routes are now maintained by the Club Alpino Italiano (CAI; Italian Alpine Club).