The Fenestrelle Fortress is the biggest alpine fortification in Europe, having a surface area of 1,300,000 m². The history of modern fortifications in the Fenestrelle area, began in 1690, when the King of France Louis XIV appointed Nicolas Catinat as commander of the French Army against the Duke of Savoy’s Army during the Nine Years' War. He understood the danger posed by the Chisone Valley for the French Army and decided to build 3 small redoubts and a fort in the Fenestrelle area. More specifically, in 1694 Nicolas Catinat obtained the approval of Louis XIV to build Fort Mutin. During the War of the Spanish Succession, this imposing fortification was besieged in August 1708 by Victor Amadeus II’s troops and conquered in 15 days.
At the end of the War of the Spanish Succession, France officially ceded Fenestrelle and the upper Val Chisone to the Duchy of Savoy as required by the Treaty of Utrecht in 1713. The treaty gave the Kingdom of Sicily to the Duchy of Savoy, making Victor Amadeus II the first king of the House of Savoy. For political reasons the Kingdom of Sicily was then exchanged with the Kingdom of Sardinia in 1720.
Fort Mutin was restored, but Victor Amadeus II found it insufficient for the protection of the Val Chisone. So he instructed military architect Ignazio Bertola to design and build a complex of forts in Fenestrelle. They were connected by a 3 km long wall, an indoor staircase of 3,996 steps unique in Europe and an outside staircase of 2,500 steps. The construction began in the summer of 1728 and ended in 1793; then it started again in 1836, ending definitively in 1850.
During the Napoleonic Era when Fenestrelle was again under the French influence, it was used as a prison by the French Empire: notable prisoners were Joseph de Maistre and Bartolomeo Pacca. The prison also held Pierre Picaud, whose story was the inspiration for Edmond Dantès, the main character in Dumas’s Count of Monte Cristo. The Kingdom of Sardinia locked political prisoners, Mazzini's supporters and common criminals in the fort, including the Archbishop Luigi Fransoni.
After the unification of Italy, around a thousand of Kingdom of the Two Sicilies soldiers were put into the fort. Several Garibaldi's and Papal States supporters were also locked up.
After the Kingdom of Italy joined the Triple Alliance in 1882, the fort was upgraded. After 1887, it became the headquarters of the Fenestrelle battalion of the 3rd Alpini Regiment.
After World War II, the fort was abandoned and left to decay, most of the available material being plundered. In 1990 a redevelopment action, guided by a group of volunteers, known as Progetto San Carlo (ONLUS) was started.
References:Celje Castle was once the largest fortification on Slovenian territory. The first fortified building on the site (a Romanesque palace) was built in the first half of the 13th century by the Counts of Heunburg from Carinthia on the stony outcrop on the western side of the ridge where the castle stands. It had five sides, or four plus the southern side, which was a natural defence. The first written records of the castle date back to between 1125 and 1137; it was probably built by Count Gunter. In the western section of the castle, there was a building with several floors. Remains of the walls of this palatium have survived. In the eastern section, there was an enclosed courtyard with large water reservoirs. The eastern wall, which protects the castle from its most exposed side, was around three metres thicker than the rest of the curtain wall. The wall was topped with a parapet and protected walkway.