The chief seaport of Rome, the Quaker City was originally scheduled to stop at Civita Vecchia but traveled directly to Naples. To avoid quarantine, Twain and friends took a French steamer to this city, then boarded a train for Rome.. Three months after Twain passed through the city it was occupied by French forces. This marks the end of the Papal States

By 1861, much of the Papal States' territory had been conquered by the Kingdom of Italy. Only Lazio, including Rome, remained under the pope's temporal control. In 1870, the pope lost Lazio and Rome and had no physical territory at all, except the Basilica of St Peter and the papal residence and related buildings around the Vatican quarter of Rome, which the new Italian state did not occupy militarily. In 1929 the head of the Italian government, at the time the Italian Fascist leader Benito Mussolini, ended the crisis between unified Italy and the Holy See by negotiating the Lateran Treaty, signed by the two parties. This recognized the sovereignty of the Holy See over a newly created international territorial entity, the Vatican City State, limited to a token territory.    https://en.wikipedia.org/wiki/Papal_States