Napoleon had 177,000 troops of the Grande Armée at Boulogne, ready to invade England. They marched south on 27 August and by 24 September were ready to cross the Rhine from Mannheim to Strasbourg. After crossing the Rhine, the greater part of the French army made a gigantic right wheel so that its corps reached the Danube simultaneously, facing south. On 7 October, Mack learned that Napoleon planned to cross the Danube and march around his right flank so as to cut him off from the Russians who were marching via Vienna. He accordingly changed front, placing his left at Ulm and his right at Rain, but the French went on and crossed the Danube at Neuburg, Donauwörth, and Ingolstadt. Unable to stop the French avalanche, Michael von Kienmayer's Austrian corps abandoned its positions along the river and fled to Munich.