By 8 February, Blücher's advancing Army of Silesia spread itself out across . Farthest to the west was Sacken's cavalry at Viels-Maisons while his infantry was at Montmirail. The Russian was in pursuit of Marshal Jacques MacDonald's 10,000-man French corps. Also following MacDonald was Yorck's corps which reached Dormans to the northeast of Montmirail. Olsufiev's 4,000-man corps was east of Sacken at Étoges. Peter Mikhailovich Kaptzevich's Russian corps and Friedrich von Kleist's Prussian corps were farther east at Châlons-sur-Marne. On 9 February, with everyone marching west, Kaptzevich and Kleist reached Bergères-lès-Vertus, Olsufiev arrived at Champaubert, Sacken got to La Ferté-sous-Jouarre, and Yorck approached Château-Thierry. Prussian staff officer Karl Freiherr von Muffling wrote that Sacken had 20,000 soldiers and Yorck's corps numbered 18,000 men while Olsufiev, Kaptzevich and Kleist together counted 19,000 troops. Another source gave Sacken strength as 16,000.