Fort de Noisy, Military fortification in Romainville, France.

Fort de Noisy is a military fortification in Romainville featuring thick stone walls and underground passages. The structure was positioned within a larger defensive system that extended around Paris to protect it from multiple directions.

Construction began in 1874 as part of the Séré de Rivières system, a response to military defeat at the hands of Prussia. This program created a ring of fortifications around Paris intended to strengthen national security.

The fort's name comes from neighbouring Noisy-le-Sec, though the site lies in Romainville. During the Algerian War it housed the auxiliary police force created to suppress the FLN in France. The No. 421 mobilisation centre was garrisoned here until the 1990s, when the DGSE's Action service and its vehicle-preparation garages moved in.

The fort remains closed to public access, though you can see its exterior walls and overall shape from several spots around Romainville. Walking around the perimeter gives you a sense of its scale and defensive design.

The fort is not abandoned: it houses part of the DGSE, France's external intelligence service, including the Action service and a technical site with garages where its vehicles are prepared. The mobilisation centre No. 421 was garrisoned here until the 1990s. The building in the photograph is the barracks of the 401st Divisional Anti-Aircraft Artillery, marked by a small round clock on the roof.