Fort de Saint-Cyr, Military fortress in Montigny-le-Bretonneux, France

Fort de Saint-Cyr is a trapezoidal Séré de Rivières fort in Montigny-le-Bretonneux. Its entrance is set into an earthen bank: a pale grey cut-stone facade with a wide arched tunnel passing through a second portal, inscribed "FORT de S.CYR" and "1874 - 1878", flanked by rough brown stone walls with barred windows. A long rough stone wall with a central arched gate and two segmental-arched openings carries the sign "SERVICE METEOROLOGIQUE".

The fort was built between 1874 and 1879 as part of a comprehensive defense system around Paris following France's defeat in the Franco-Prussian War. This fortification represented a direct response to the need for protecting the capital against future attacks.

The fort houses a major film archive storing thousands of works from French cinema history. This unexpected use of a former military building shows how places can transform their purpose entirely.

The fort lies in Montigny-le-Bretonneux, in the Yvelines, and is not a site open to casual visitors: it is a working conservation centre for the Médiathèque du patrimoine et de la photographie and the Cinémathèque française. Access to the grounds and buildings is therefore by arrangement, not year-round guided tours. The entrance on the earthen bank is marked "FORT de S.CYR" with the dates 1874 - 1878.

The fort's twin 155 mm Mougin turret still stands, though its guns were removed. Since 1982 the site has housed photographic archives of the Médiathèque du patrimoine et de la photographie, and 40,000 copies from the Cinémathèque française collection were stored here thanks to Henri Langlois.