September 10: The Italian army under the command of General Raffaele Cadorna and under the ultimate direction of King Victor Emanuel II crossed the papal frontier, and by September 20 Rome and Latium were annexed to the Kingdom of Italy.
Quirinal Palace, formerly the pope’s residence, became the royal palace of the King of Italy. Pius IX was pope at the time.
59 years later, the Lateran Treaty of 1929 created the State of the Vatican City, forming the current sovereign territory of the pope.