The French army was defeated at the Battle of Charleroi and managed to pass only one regiment into Namur as a reinforcement. The forts were destroyed by the bombardment, some being demolished by conventional heavy artillery rather than the siege guns, due to flaws in the concrete protection encasing the forts. The last of the Belgian fortress troops were forced to surrender on 25 August, after the survivors of the Belgian 4th Division had withdrawn to the south through the French Fifth Army and eventually joined the Belgian field army at Antwerp during the siege.