Fort de Cormeilles-en-Parisis, Montigny-lès-Cormeilles

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. ()