Fort d'Ivry, Military fortification in Ivry-sur-Seine, France

Fort d'Ivry is a military fortification in Ivry-sur-Seine featuring five bastions and stone walls that conceal an extensive network of underground passages. These passages extend for several kilometers beneath the structure, forming a vast subterranean system.

Fort d'Ivry was built from 1841 to 1846 under Louis-Philippe, on plans by François Nicolas Benoît Haxo, as one of the sixteen detached forts of the Thiers Wall ring around Paris. In 1870-71 a Fusiliers Marins battalion from Brest manned it with 94 guns; the 6th Prussian Corps occupied it from 29 January to 20 March 1871. After the Franco-Prussian War it was upgraded under the Séré de Rivières program.

The fort's name comes from Ivry-sur-Seine, the suburb it was built to defend. Since 1946 it has housed the ECPAD, the defence ministry's audiovisual archive, which keeps about 3.5 million photographs and 16,800 films from 1900 onward. In its ditches, some 250 allotment gardens cover 7.5 hectares, classed as a sensitive natural area by Val-de-Marne since 1991.

The fort is not currently open to visitors as it houses a military facility that stores archives. While you cannot enter the building, you can view the exterior structure and surrounding fortification from outside.

The fort's more than two kilometres of underground passages were added between 1852 and 1860, with ceilings six metres thick. During the Paris Commune, the Communards evacuated the fort on the night of 24/25 May 1871, blowing up munitions and destroying nine casemates; repairs in 1872 added two more barracks.