Fort de Pontisse The Fort de Pontisse 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 refuge for bats , which may be visited during summer months . Description . The Fort de Pontisse is located about northeast of the center of Liège . Flémalle overlooks the Meuse valley and the Albert Canal downstream from Liège . The fort was built as an irregular trapezoid . 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 weapons and could not withstand heavier artillery . Armament . Pontisse ' s armament included two turrets with a single 21 cm Krupp gun , a 15 cm turret with twin guns and two 12 cm turrets 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 . Eight 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 Liers and Fort de Barchon across the river . 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 . 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 . Pontisse was the first fort to come under bombardment from 42 cm artillery . It held out until 13 August 1914 , when it surrendered , unable to resist any longer . The Germans improved Pontisse with better sanitary arrangements , ventilation and reinforced concrete in 1916 . The Liège forts were reoccupied by the Belgian army in 1918 after the armistice . Fortified Position of Liège . Pontisse ' s 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 . The 57mm guns were replaced with machine guns . As the most northern fort in PFL IV , it was tasked to support Fort Eben - Emael . A flanking bunker was built to survey the Laveau ravine and to serve as an alternate exit and as a source of ventilation air , in contrast to most of the other Liège forts , which used ventilation towers . Second World War . In May 1940 Pontisse was garrisoned by 223 men under the command of Captain - Commandant Fernand Pire . Following the successful German assault on Fort Eben - Emael to the east on May 11 , Pontisse provided fire support for Belgian field units for the next few days , including firing on the area around Eben - Emael after Eben - Emael ' s surrender . Pontisse surrendered in its turn on May 18 following air attack that destroyed the 105mm turret and damaged the 76mm turrets . Pontisse was in any case almost out of ammunition . Present . Pontisse was used as an army munitions depot after the war , then by a private munitions firm for the same purpose . It was stripped of its equipment by a salvager in the 1950s . The fort has been unoccupied since 1993 . It is presently maintained as a refuge for bats during the winter months . It may be visited in the summer by arrangement .