Having crossed the Niemen river with his Corps, Nansouty would continuously march under the command of Joachim Murat during this campaign, preceding the advance of the army and taking Wilna as they advanced. Despite marching constantly alongside Murat and Emperor Napoleon, Nansouty's Ist Corps of cavalry reserve saw little action, combating brilliantly in a vanguard action at Ostrovno and then briefly at Vitebsk. An incident involving some of Nansouty's light cavalry occurred during the combat at Vitebsk, when the 8th Hussars and 16th "Chasseurs à cheval" turned and fled before the Russian light horse. This was evidence that the division of Bruyères, of which they were a part, had been much used by always being placed at the vanguard of the army, resulting in the loss many of the best and bravest troopers. Despite Nansouty's best efforts, the extremely long and exhausting marches, the torrential rains and the absence of proper fodder took their toll on the Ist Cavalry Corps, with numbers reduced to half by this time. Additionally, just like the other Cavalry Corps commanders, Nansouty rarely had all his troops under direct control, which led to cavalry being used improperly at times.