The Fort de Cormeilles-en-Parisis was constructed between 1874 and 1877 as part of a new plan for the defense of Paris developed by General Raymond Adolphe Séré de Rivières, near the town of Cormeilles-en-Parisis. During the Franco-Prussian War, German troops had used the hill upon which the fort sits as a spotting and firing location, ideal for the siting of new rifled guns whose range was increased over old-fashioned smooth-bore guns. These weapons could attack Paris from Cormeilles, so a new outer ring of forts had to be built outside the first ring of forts built in 1840-1860 to deny the area to enemy gunners. The Séré de Rivières system was designed as a response to these technological innovations, and to the loss of French territories in Alsace and Lorraine.