Presumably a reference to The Battle of Liège (August 1914). The Battle of Liège was the opening engagement of the German invasion of Belgium and the first battle of the First World War. The attack on Liège, a town protected by the fortified position of Liège, a ring fortress built from the late 1880s to the early 1890s, began on 5 August 1914 and lasted until 16 August, when the last fort surrendered. The siege of Liège may have delayed the German invasion of France by four to five days. For a British perspective see PC_PunchWWI_0009.