Siege of Turin ( 1640 ) The 1640 siege of Turin was a major action in two distinct wars : the Franco - Spanish War ( 1635 ) and the Piedmontese Civil War . Thomas of Savoy and his supporters had seized the city of Turin in 1639 , but French troops supporting the Regent Christine continued to hold the citadel . Under normal conditions in this period , it was not possible for a town to be held against a hostile citadel , but the anti - French forces managed to construct barricades that contained the French in the citadel , and spent the winter of 1639 – 40 under an uneasy truce . On 10 May , the French army under Harcourt and Turenne , supported by troops raised by Regent Christine , invested Turin , and thus started what became one of the most famous ( and complicated ) military events of the 17th century . Double siege . After pushing in most of the defenders ' outposts and building the usual lines of investment , the besiegers opened fire on 22 May . On 31 May a Spanish army under the governor of Milan , Diego Felipez de Guzmán , Marquis of Leganés , approached , but despite his numerical superiority dared not make a full - scale assault on Harcourt ' s lines , so he himself began to entrench around the French , starting a weeks - long conflict over individual posts but , despite constant pressure from Prince Thomas , only once risking an outright battle , in mid - July ( 14 July according to Saluzzo , 11 July according to Hanotaux and Bérenger ) , when he was thoroughly repulsed . The situation was particularly complicated in that Prince Thomas in Turin continued for weeks to hold some posts outside the city , ensuring some contact with the Spanish and a line of communication for supplies ; the last such post fell to Harcourt late in July , and after this , food shortages began to hit the population and garrison - forage for horses ran out first , and Thomas twice attempted sorties , on 23 and 31 July , intended to enable his cavalry to escape , but failing both times . Harcourt was never completely cut off by Leganés from his lines of communication , and he was of course in contact with the citadel , but it is fair to agree with the traditional view that this had now become a four - layered siege : French troops still in the citadel were under attack by Thomas in the city , who was himself besieged by Harcourt and the French army , who was himself besieged by Leganés . It is sometimes suggested that Leganés tried to fire supplies over the French camp into the city , but this may be a legend , built on the fact that the Spanish did maintain written contact with Prince Thomas by messages placed inside cannon - balls and fired over the French heads . Surrender . Turin eventually had to consider surrender , and Prince Thomas , who had maintained on - off talks with the French and the Regent throughout the siege , opened negotiations with Harcourt , who made an agreement contrary to orders - if the French historian Hanotaux is to be believed , he was unaware of orders en route from Paris that he was to accept nothing from Thomas except pure surrender as a prisoner or agreement to enter French service ; according to Saluzzo , Harcourt knew that Cardinal Richelieu ' s agent Mazarin was on his way with orders but wanted to avoid sharing the glory of a victory with anyone else so hastened to reach a settlement before Mazarin arrived . Whatever the cause , Harcourt agreed a cease - fire on 16 September and granted Thomas honourable terms in the capitulation signed on 20 September , and on 24 September Thomas marched out with his troops and withdrew to Ivrea .