The Grand Ouvrage fort at Flaut is part of the Alpine section of the Maginot Line. It was built between 1931 and 1935 along with Gordolon to guard the Vésibie Valley. Flaut was garrisoned by around 300 soldiers.
The layout is typical of other forts, with barracks, magazine and plant rooms along an entrance corridor. This leads to cross passages which link three artillery and one infantry block. A number of observation posts reported in to the fort. Some of the passages are steeper than usual, which would have needed an increased effort by the soldiers to propel the loaded ammunition carts. Another unusual feature was a compressor found within the kitchen, whose purpose is unclear.
In 1940 Flaut saw action against the invading Italian forces. When visited in 2003, some of the features were in reasonably good order but the site has since deteriorated and is fully abandoned.