Fort de Loncin, Military fort and museum in Ans, Belgium

Fort de Loncin is an isosceles-triangle fort in Ans, 7 km west of Liège, built 1881–1884 by General Henri Alexis Brialmont of unreinforced concrete. Its base measures 300 m and its sides 235 m, encircled by a ditch 6 m deep and 8 m wide. The central massif held two 21 cm howitzer turrets, a double 15 cm gun turret, two double 12 cm turrets and four single 57 mm turrets, with nine rapid-fire 57 mm guns in the ditch casemates. A rough concrete sculpture of a face stands near the entrance.

The fort was built in the 1880s to defend Liege but was destroyed in 1914 during the German advance into Belgium. German artillery fire triggered an explosion in the ammunition store that damaged the structure and killed many garrison members.

The fort is a war grave and national necropolis: 350 of the 550-man garrison were killed on 15 August 1914 and most remain under the collapsed concrete. King Philippe declared it a nécropole nationale on 3 August 2014, and since 2023 it has been UNESCO World Heritage as a World War I grave and memorial site. A military cemetery and memorial stand on the grounds.

Access is by marked pathways and most areas are walkable for visitors, though some underground chambers can be slippery and confined. It is best to wear sturdy shoes and be prepared for uneven surfaces and narrow passages throughout the site.

The ruins still show visible scars from artillery bombardment with deep craters and cracks across the concrete structure. Some soldiers who died during the battle were entombed within the rubble and remain there to this day.