The French army was now preparing to cross the Alps a second time, under the command of Trivulce.

Louis XII had come as far as Lyons in the company of Caesar Borgia and Giuliano della Rovere, on whom he had forced a reconciliation, and towards the beginning of the month of May had sent his vanguard before him, soon to be followed by the main body of the army.

The forces he was employing in this second campaign of conquest were 1600, lances, 5000 Swiss, 9000 Gascons, and 3500 infantry, raised from all parts of France.

On the 13th of August this whole body, amounting to nearly 15,000 men, who were to combine their forces with the Venetians, arrived beneath the walls of Arezzo, and immediately laid siege to the town.
Ludovico Sforza's position was a terrible one: he was now suffering from his imprudence in calling the French into Italy; all the allies he had thought he might count upon were abandoning him at the same moment, either because they were busy about their own affairs, or because they were afraid of the powerful enemy that the Duke of Milan had made for himself.

Maximilian, who had promised him a contribution of 400 lances, to make up for not renewing the hostilities with Louis XII that had been interrupted, had just made a league with the circle of Swabia to war against the Swiss, whom he had declared rebels against the Empire.