Fort de Liers The Fort de Liers 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 . Liers was never upgraded like the other forts of Liège . It is now used as a test site for aircraft engines and is not accessible to the public . Description . The Fort de Liers is located about north of the center of Liège , near Liers . one of the smaller Liège forts , Liers forms an isosceles triangle . 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 . 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 . Liers ' armament included a turret with a single 21 cm gun , a 15 cm turret with twin guns and a 12 cm turret with two guns , all for distant targets . 57mm gun turrets were provided for local defense . The fort also mounted an observation turret with a searchlight . Rapid - fire 57mm guns were provided in casemates for the defense of the ditches , as well as in turrets . 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 . 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 . Lies was heavily bombarded starting 13 May . Liers ' neighbor , the Fort de Pontisse , surrendered the same day , allowing the Germans to concentrate on Liers , firing from the fort ' s vulnerable rear . Liers surrendered on the 14th , with the interior of the fort uninhabitable due to dust , gun gas and sewage . Second World War . Liers was not upgraded in the 1930s as part of the Fortified Position of Liège . The Belgian Army used the fort to store munitions . Post - war and present . Following the war the Fort de Liers was sold by the military to Fabrique Nationale ( FN ) for one franc in 1949 , FN eventually becoming Techspace Aero . The fort is used as a testing area of aircraft engines by Techspace Aero , whose plant adjoins the fort , and is not accessible to the public . The fort ' s shape remains discernible , with sound control ducting closely adjoining the central massif of the fort .