The Siege of Florence took place from 24 October 1529 to 10 August 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.