During the Siena War where the Sienese and French armies faced each other against the Florentine and Spanish armies, besieged Siena on August 2, 1554 and surrendered the city in April 1555, Porto Ercole still remained to be conquered, where the French commander Charles de Carbonnières, after having awaited the arrival of Marshal Piero Strozzi, he surrendered on June 18, 1555.