After the September Convention of 1864, Antonelli organised the Legion of Antibes to replace French troops in Rome and in 1867 secured French aid against Giuseppe Garibaldi's invasion of papal territory. Upon the reoccupation of Rome by the French after the Battle of Mentana on 3 November 1867, Antonelli again ruled supreme, but after the entry of the Italians in 1870, he was obliged to restrict his activity to the management of foreign relations. With the Pope's approval, he wrote the letter requesting the Italians to occupy the Leonine City in which the Italian government had intended to allow the pope to keep his temporal power and obtained from the Italians payment of the Peter's pence (5,000,000 lire) remaining in the papal exchequer, as well as 50,000 scudi, the only installment of the Italian allowance (subsequently fixed by the Law of Guarantees, 21 March 1871) that was ever accepted by the Holy See.