When the Pope became a prisoner in his own city after a brief siege
On September 20, 1870, Italian forces breached the walls of Rome, ending centuries of papal temporal power. Pope Pius IX refused to accept the new reality, declaring himself a prisoner in the Vatican. This standoff, known as the Roman Question, would define Italian politics for nearly sixty years.
The capture of Rome was the final act of the Risorgimento, the movement to unify Italy. By 1861, the Kingdom of Italy had been proclaimed, but Rome remained under the control of the Papal States, protected by a French garrison. The situation shifted in 1870 when the Franco-Prussian War forced Napoleon III to recall his troops. With the French Empire collapsing after the Battle of Sedan, the newly formed Italian government saw an opportunity to claim its capital.
King Victor Emmanuel II initially sought a peaceful entry, sending Count Gustavo Ponza di San Martino to negotiate with Pope Pius IX. The Pope, however, was defiant, famously predicting that the Italians would never enter the city. When negotiations failed, General Raffaele Cadorna led 50,000 Italian troops against a defense force of roughly 13,000, which included the Swiss Guard and international volunteers. On September 20, 1870, artillery fire breached the Aurelian Walls near Porta Pia, allowing the Italian army to enter.
Following the city's fall, a plebiscite on October 2, 1870, showed overwhelming support for union with Italy. Despite this, the Pope excommunicated the invaders and rejected the Law of Guarantees, which offered him sovereign prerogatives and financial support. He remained in the Vatican, refusing to recognize the Italian state. This impasse lasted until 1929, when the Lateran Pacts, signed by Benito Mussolini and Cardinal Pietro Gasparri, finally settled the Roman Question by establishing the Vatican City as an independent sovereign state.
Source: Capture of Rome
