In mid-October 1524, Francis himself crossed the Alps and advanced on Milan at the head of an army numbering more than 40,000. Bourbon and Pescara, their troops not yet recovered from the campaign in Provence, were in no position to offer serious resistance. The French army moved in several columns, brushing aside Imperial attempts to hold its advance, but failed to bring the main body of Imperial troops to battle. Nevertheless, Charles de Lannoy, who had concentrated some 16,000 men to resist the 33,000 French troops closing on Milan, decided that the city could not be defended and withdrew to Lodi on 26 October. Having entered Milan and installed Louis II de la Trémoille as the governor, Francis (at the urging of Bonnivet and against the advice of his other senior commanders, who favored a more vigorous pursuit of the retreating Lannoy) advanced on Pavia, where Antonio de Leyva remained with a sizable Imperial garrison of about 9,000.