On the morning of the 21st, French Commander-in-Chief Joseph Joffre reported to Lanrezac (and to the BEF) that German troops were moving west. In accordance with Plan XVII, the Third and Fourth armies further south were to move towards, respectively, Arlon and Neufchâteau, then seek to attack enemy forces in Belgian Luxembourg. The Fifth Army was ordered to cover the Meuse up to Namur, and the British were to cooperate in this action by moving in the general direction of Soignies, north-east of Mons. In accordance with this, Lanrezac positioned the Fifth Army on the Sambre, and reported his actions to Joffre later in the day, around 12:30. Unbeknownst to him at the time, German elements had clashed with his vanguards, between Namur and Charleroi. Lanrezac was made aware of this by a report from General Augustin Michel, commander at Namur, received at 14:00. Lanrezac was told by General Headquarters around 16:00 that the Germans were still moving west, and in consequence ordered his aviation to reconnoitre enemy troop movements and informed his subordinates that they should "be ready to launch an attack [...] by crossing the Sambre, towards Namur and Nivelles." At 20:00, having reported only minor action on the 10th Corps front to Joffre at 19:00, Lanrezac was instructed by the latter that he had total discretion to decide of the appropriate moment to start his offensive.