 Complete the following phrase:  The Fort de Pontisse is one of twelve forts built around Liège, Belgium, in the late 19th century. The overall Fortified Position of Liège was a constituent part of the countrys National Redoubt. Fort de Pontisse 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 