was pulled down in 1919. The Boulevard Périphérique today marks the general course of the wall. Several of the forts survived, and became centers for more modern military installations. The Ministry of Defense occupied Fort Issy until the early 2000s. The site was acquired by the city of Issy-les-Moulineaux in 2006. The site was fully demilitarized in 2009. Eco-district The fort was returned to civilian use in 2009, and the town began a major project to build a "digital eco-district". The eco-district was completed in 2013. It contains 1,623 dwellings of which 330 are social housing, a bowling alley, of shops and public facilities, two schools, a swimming pool and a multi-use space, Le Temps des Cerises . The buildings are surrounded by trees, walks, squares and playgrounds. An underground network is used for waste collection. The buildings are rated BBC (Bâtiment Basse Consommation: Low Consumption Building) and use thermal insulation and renewable geothermal heat to minimise CO2 emissions. The complex uses a geothermal heat network with two wells over deep that reach the Early Cretaceous Albian aquifer. The Albian has a temperature of , which is ideal for low-temperature heat networks like that of Fort d'Issy. One well, almost deep, is used to pump up the water to a heat exchange substation. The water, now with a temperature of about , is returned in full to the aquifer by a well deep. The two wells are apart at their feet to avoid thermal recycling, and the system is sealed to prevent any contamination of the water. Within the buildings heat pumps deliver water at to heat the floors and hot tap water at . Notes Sources Former military buildings and structures Fortifications of Paris 1840 establishments in France 2009 disestablishments in France Military installations established in 1840 Military installations closed in 2009