Elected as a moderate progressive, he relaxed press censorship, freed political prisoners, set up a council of ministers which included laymen, and opened negotiations for an Italian customs union. After the Revolutions of 1848 his Prime Minister was murdered and Pius himself fled in disguise. On the establishment of a Roman republic Pius appealed to the French to come to his aid, and, with their help, he re-entered Rome, which retained a French garrison until 1870. In that year Italian forces occupied Rome, which was then incorporated into the kingdom of Italy. Despite government assurances, Pius saw himself as a prisoner in a secular state, and never set foot outside the Vatican again. In 1854 he defined the doctrine of the Immaculate Conception of the Virgin Mary (the Mother of Jesus Christ) and encouraged the Marian cult. He presided over the First Vatican Council (1869–70), which proclaimed the infallibility of the Pope when speaking ex cathedra.