Following the fall of the forts at Liege in Belgium on 16 August 1914, King Albert I ordered a withdrawal of Belgium's remaining 65,000 troops to Antwerp, another fortress city (along with Namur).
Together with 80,000 garrison troops, Antwerp's ring of 48 outer and inner forts presented formidable opposition to von Kluck's German First Amy's flank. Von Kluck had chosen to bypass Antwerp in the Germany army's advance through Belgium and into France. Nevertheless, the presence of so many troops at its flank presented a constant threat.
This danger transpired into sorties conducted from the forts on 24-25 August and 9 September, designed by the Belgians to distract the Germans from their attack upon the British and French at the Battles of Mons and Charleroi. Effective to a degree, von Kluck was obliged to detach four divisions solely to face attacks from Antwerp. Following the attack on 9 September however the German High Command, led by the German Chief of Staff Helmuth von Moltke in Berlin, determined to capture the Antwerp forts.
Before this could be done however, action at the Marne distracted all German attention to their advance upon Paris, followed after the Marne action by a retreat to the Aisne.