 In 1870 France was partly occupied by the Prussian Army.Following this defeat, France put in place the Séré de Rivières system of fortifications to modernize its fortifications and to adjust its defensive strategy to the new borders imposed in 1871.The portion of the system surrounding Paris amounted to 18 forts, 5 redoubts and 34 batteries constructed between 1874 and 1881, of which the Fort du Trou d'Enfer is a part.