The Siege of Florence took place from October 24, 1529 to August 10, 1530, at the end of the War of the League of Cognac. A large Imperial and Spanish army under Philibert of Châlon, Prince of Orange and Pier Maria III de' Rossi surrounded the city, and, after a siege of nearly ten months, captured it, overthrowing the Republic of Florence and installing Alessandro de' Medici as the ruler of the city.