Fort du Risoux, Military fort in Les Rousses, France.

Fort du Risoux is a first-generation Séré de Rivières fort built 1880–1884 at 1273 m on a promontory of the Risoux forest above Lac des Rousses. Its irregular pentagon plan is enclosed by ditches defended by two double caponiers and one single caponier, with 20 cm openings for grenades. The casernement forms two facing groups of barrack rooms around a central courtyard, and 16 artillery platforms are served by a rampart road. The stone retaining wall shows a row of arched openings, with a large arched entrance door at the centre.

Fort du Risoux was built from 1880 to 1884 as a first-generation Séré de Rivières fort, part of the Jura curtain defending the Rousses stronghold, 3 km north of Fort des Rousses. It was declassified in 1892 and played no military role, though it later belonged to the Jura fortified sector of the Maginot Line. After World War II it served as pasture, then for explosives training until June 1997, and left the military domain by decree on 1 February 1999.

The fort's name honours Commander Guyot, hence its short form fort Guyot. After its 1892 declassification it served as pasture for decades, then until June 1997 the commando training centre at fort des Rousses used it for explosives-handling practice. Today the local shooting association has installed sport shooting ranges inside the fort.

Access is via the 3 km strategic path that starts north of Les Rousses village and climbs to the fort at 1273 m. The interior has been closed to visitors since restoration work between 2005 and 2007, so the ramparts, ditches and the two caponnières are seen from outside. The site is also used by a local shooting club, so check before walking near the ranges.

During construction, workers used a rope and pulley system to haul heavy materials up the steep slope from the lake below. This makeshift setup, which builders called 'la ficelle', left physical traces on the landscape that remain visible to explorers who know where to look.