The Fort du Trou-d'Enfer, also known as the Réduit du Trou-d'Enfer, is one of the fortifications of Paris, It is located in Marly-le-Roi, in the departement of Yvelines. The fort was built between 1878 and 1881 for a garrison of 800 men. It was termed a réduit for its position surrounded by several smaller batteries. The fort was occupied by the Germans during World War II, who blew up their ammunition when they evacuated the fort in August 1944, damaging the fort. The fort is named for the farm on whose land it sits, the ferme du trou-d'enfer, literally "Hellhole Farm."