Fort de Flémalle The Fort de Flémalle is one of twelve forts built as part of the fortifications of Liège in the late 19th century in Belgium . It was built between 1881 and 1884 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 . The fort was heavily bombarded by German artillery in the Battle of Liège . Attacked in both World War I and World War II , the fort has been preserved as a museum . Description . The Fort de Flémalle is located about southwest of the center of Liège . Flémalle overlooks the Meuse valley upstream from Liège . The fort was built as an irregular trapezoid , almost triangular . A deep by ditch encircles the fort . The principal armament was concentrated in the central massif . 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 fort is one of the larger Liège forts . With the exception of the Fort de Loncin , the 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 Liège ) , with lesser protection than the two " 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 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 . Flémalle ' s armament included two turrets with a single 21 cm Krupp gun , a15cm turret with twin guns and two 12 cm turret with two Krupp guns , all for distant targets . Four 57mm gun turrets were provided for local defense . The fort also mounted an observation turret with a searchlight . Eleven rapid - fire 57mm guns were provided in casemates for the defense of the ditches and the postern . 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 the neighboring Fort de Loncin and Fort de Liers . The guns were fired using black powder rather than smokeless powder , producing choking gas in the confined firing spaces that spread throughout the fort . First World War . In 1914 Flémalle was commanded by Captain - Commandant Falize with five officers and 150 men . Liège first came under attack on 6 August 1914 . When the Liège ' s fortifications proved unexpectedly stubborn , the Germans brought heavy siege artillery to bombard the forts with shells far larger than they were designed to resist . Flémalle was one of the last forts to come under heavy bombardment , and was the last of the Liėge forts to surrender . Following the explosion of the Fort de Loncin , the Germans sent delegations to the last two holdouts , Flémalle and the Fort de Hollogne , emphasisizing the consequences of continued resistance . Flémalle at 0930 on 16 August , two hours after Hollogne . Fortified Position of Liège . Flémalles armament was upgraded in the 1930s to become part of the Fortified Position of Liège II , which was planned to deter a German incursion over the nearby border . The armament was upgraded with new guns in the turrets and an anti - aircraft battery . This was accompanied by improvements to ventilation , protection , sanitary facilities , communications and electrical power . Armament included a machine gun turret , a twin 105mm gun turret , a turret with a single 150mm gun , and four single 75mm guns in retractable turrets . The 57mm guns were replaced with machine guns . Six anti - aircraft guns were also provided . Second World War . In 1940 Flémalle was commanded by Captain - Commandant Barbieux , with five officers and about 150 men . Following the successful German assault on Fort Eben - Emael to the east , Flémalle provided fire support for Belgian field units for the next few days . On 15 May the fort came under aerial bombing attack , destroying the gun turrets . The next day German ground forces attacked . Unable to mount an effective resistance , the fort surrendered . Present . Flémalle was partly stripped of its equipment during the German occupation , and again by a salvager in the 1960s . The fort has been maintained by a preservation association since 1992 , which has established a museum in the fort .