Facing Mount Orsiera, next to Fenestrelle, a small town in the Turin area, eyes of tourists meet the main and the biggest alpine fortification in Europe. It is an impressive view offered by this beautiful defensive work, which the kings of Sardinia built in the 18th century against France. A great Piedmontese wall, a wonderful stone construction which spans a ravine of 650 metres and has a surface area of 1,350,000 square metres. It is not only one block, but a group of fortresses (San Carlo, Tre Denti, Valli), powder-store rooms, batteries and strong gunners. All this is linked through the immense staircase which stretches 4,000 steps from San Carlo to Valli, with five external and twelve internal drawbridges, inside a man-made tunnel. In the Chisone valley, the first stone used to strengthen the building was placed as a barrier against the French. This work of art was began in 1728, when Victor Amadeus II, the fox and lion of Savoy, entrusted the project to Ignazio Bertola from Exilles, a talented military architect. The great wall grew near the Pra Catinat plateau, at a height of 1,800 metres. And, after 120 years of work, it reached the present Road 23. Soon, the king abdicated and he transfered the works to his son Carlo Emanuele III and to Varino de la Marche, who succeeded Bertola. A lot of engineers such as Rana and Marchiotti collaborated to erect the forts, co-operating with the many Savoy's sovereigns until Carlo Alberto finished the building in 1850. Made after the Utrecht treaty, it was never involved in a battle. For this reason in 1747 the war was fought on Assietta's hill, above the fortress, because the French were intimidated by the fortress's strength. It became also a political prison: with the occupation by Napoleon, it became place of suffering, where famous political and religious men (such as the cardinal Pacca and the writer De Maistre) were imprisoned. The years later, the fortification became a concentration camp; until 1920, four hundred men were imprisoned because of crimes committed during the war. Between the two wars, it lost relevance: first it became artillery deposit and then the site of partisans' fights. In 1940 the Italian army abandoned it. Only now the construction has been revived: in 1990 a group of enthusiasts founded the Progetto San Carlo Onlus Association. They also organised the first guided tours, they proposed many performances such as stand up comedies and cinema. Thanks to the Piedmont Region and the Turin Province it is regaining its ancient dignity and it is becoming an interesting historical and political site. Several interventions have already been made. It is situated in a Regional Park, and it has been the Turin Province representative monument since 1999.