Dawn broke misty on 21 August and no air reconnaissance was possible until the afternoon. The BEF began to advance northwards from Maubeuge towards Mons, despite reports from aircrew that a column of German troops "stretched through Louvain as far as the eye could see". At Maubeuge, news arrived of the fall of most of the Fortified Position of Namur in Belgium and placards put up on the town walls ordering preparations for a siege began an exodus of 25,000 civilians. British aircraft arrived on 22 August and the passage of a Scottish regiment raised civilian morale briefly, only to be dashed by reports that German troops had crossed the Sambre at Charleroi. From 17 August, Maubeuge came under the command of General Charles Lanrezac, commander of the Fifth Army and at the Battle of Charleroi (21–23 August) the Fifth Army and the BEF were defeated and forced to retreat. The ministerial instructions of 1910 had envisaged that Maubeuge might stand a short siege while covering the concentration of the field armies, not indefinite isolation after a retreat by the field armies. Lanrezac considered adding the regular and reserve regiments to the Fifth Army but rejected the idea. The Maubeuge garrison cut the rail lines and engineer detachments blew the rail bridges at Jeumont, Berliaumont and Fourmies towards the Belgian frontier.