Lasalle joined the French Army for its 1809 Campaign along the Danube. He arrived just prior to Napoleon's push across the Danube at Aspern-Essling and was sent to scout the location of the Austrian army. The first stage of the operation began on 13 May 1809, laying a bridge of boats over the first arm of the Danube to Lobau. Then, the advance guard and Lasalle's light cavalry would pass into Lobau, together with the material needed to bridge the second arm to the left bank. As soon as this was finished, Molitor’s division and Lasalle's four light cavalry regiments passed over and Lasalle's horsemen fanned out into the plain. There were no travelers or couriers to be intercepted there, as there had always been in Prussia and Spain; consequently, Lasalle's officers had nothing to go on but the evidence of their own eyes and ears.