Hostilities now flared up across northern France. On Henry's orders, Sir John Wallop crossed the Channel to Calais with an army of 5,000 men, to be used in the defense of the Low Countries. The French, under Antoine de Bourbon, Duke of Vendôme, had captured Lillers in April; by June, d'Annebault had taken Landrecies as well. Wilhelm of Cleves openly joined the war on Francis's side, invading Brabant, and fighting began in Artois and Hainaut. Francis inexplicably halted with his army near Rheims; in the meantime, Charles attacked Wilhelm of Cleves, invading the Duchy of Jülich and capturing Düren.