Fort de Malonne The Fort de Malonne is one of nine forts built as part of the Fortifications of Namur in the late 19th century in Belgium . It was built between 1888 and 1892 according to the plans of General Henri Alexis Brialmont . Contrasting with the French forts built in the same era by Raymond Adolphe Séré de Rivières , the fort was built exclusively of unreinforced concrete , a new material , rather than masonry . In 1914 the fort was heavily bombarded by German artillery in the Battle of Namur . Malonne was upgraded in the 1930s to become part of the fortified position of Namur in an attempt to forestall or slow an attack from Germany . It saw action in 1940 during the Battle of Belgium , and was captured by German forces . The fort is presently part of a nature preserve and is a habitat for bats . Description . The Fort de Malonne is located about southwest of the center of Namur . The fort forms an irregular rectangle in plan . A deep by ditch encircles the fort . The ditches were defended in enfilade by 57mm guns in casemates resembling counterscarp batteries , firing at shot traps at the other end of the ditch . The principal armament was concentrated in the central massif , closely grouped in a solid mass of concrete . Belgian forts made little provision for the daily needs of their wartime garrisons , locating latrines , showers , kitchens and the morgue in the fort ' s counterscarp , a location that would be untenable in combat . This would have profound effects on the forts ' ability to endure a long assault . The service areas were placed directly opposite the barracks , which opened into the ditch in the rear of the fort ( i . e . , in the face towards Namur ) , with lesser protection than the front and " salient " sides . The Brialmont forts placed a weaker side to the rear to allow for recapture by Belgian forces from the rear , and located the barracks and support facilities on this side , using the rear ditch for light and ventilation of living spaces . In combat heavy shellfire made the rear ditch untenable , and German forces were able to get between the forts and attack them from the rear . The Brialmont forts placed a weaker side to the rear to allow for recapture by Belgian forces from the rear , and located the barracks and support facilities on this side , using the rear ditch for light and ventilation of living spaces . In combat heavy shellfire made the rear ditch untenable , and German forces were able to get between the forts and attack them from the rear . The Brialmont forts were designed to be protected from shellfire equaling their heaviest guns : 21 cm . The top of the central massif used of unreinforced concrete , while the caserne walls , judged to be less exposed , used . Under fire , the forts were damaged by 21 cm fire and could not withstand heavier artillery . Armament . Malonne ' s armament included a rotating turret with a single 21 cm gun , a15cm turret with twin guns and two 12 cm turrets with single guns , all for distant targets . Three retractable 57mm gun turrets were provided for local defense . The fort also mounted an observation turret with a searchlight . Six rapid - fire 57mm guns were provided in casemates for the defense of the ditches and the postern , as well as two mobile guns . The fort ' s heavy guns were German , typically Krupp , while the turret mechanisms were from a variety of sources . The fort was provided with signal lights to permit communication with neighboring forts . The guns were fired using black powder rather than smokeless powder , producing choking gas in the confined firing spaces that spread throughout the fort . Fortified Position of Namur . Malonne ' s armament was upgraded in the 1930s to become part of the Fortified Position of Namur , which was planned to deter a German incursion over the nearby border . The 21 cm turret was replaced with longer - range 15m turrets , the 15 cm turret was replaced by a turret with machine guns and grenade launchers , and the 12 cm turrets were replaced with turrets containing twin 105mm guns . Protection was substantially increased . This was accompanied by improvements to ventilation , protection , sanitary facilities , communications and electrical power . Second World War . In 1940 during the Battle of France Malonne was commanded by Captain - Commandant Demaret . The fort surrendered to the Germans on 21 May 1940 , after exhausting its ability to fight back . Before surrendering the garrison sabotaged what arms were left intact . The garrison ' s surrender was accepted by the Germans with military honors . Present . The fort ' s site is a nature preserve . Since 1991 the fort has been closed to public access and is a protected habitat for bats . The site is administered by the " Amicale pour la sauvegarde du Fort Malonne " .