[1] The Legion was recruited under direction of Pope Pius IX's secretary of state, Giacomo Antonelli, following the September Convention of 1864, to replace French troops garrisoned in Rome, during the closing phase of Italian unification, the Risorgimento.
After the battle of Mentana, fought on 3 November 1867 between French-Papal troops and the Italian volunteers led by Giuseppe Garibaldi, it became public knowledge that the "Legion" was composed of French Imperial recruits from Antibes lying on the Mediterranean coast close to the border with Piedmont: their "services to the Pope were rendered as services to the French Empire," the former Prime Minister of Italy, Francesco Crispi recalled in 1891.
"It is singular that on the dead bodies were found livrets (pay books) from French regiments, to which every one of these men belonged, with the number of his matriculation, and with formula of the oath of fidelity to the Emperor.
[3] Cardinal Antonelli continued to call for the Catholic powers of Europe to come to the aid of the Pope, but there was no response.
During the Franco-Prussian War, any soldier desiring to return to fight for France could do so, with the fifth and sixth companies of each battalion disbanded.