September 20
Italian Forces Capture Rome and Complete Unification
On September 20, 1870, Italian forces under General Raffaele Cadorna breached Rome’s ancient walls and entered the city, ending centuries of papal rule over the Papal States and completing the territorial unification of Italy.
Summary
Following the proclamation of the Kingdom of Italy in 1861, Rome remained under papal control as the last major holdout of the Papal States, protected earlier by French troops. With France distracted by the Franco-Prussian War, Italian forces under General Raffaele Cadorna advanced on the city. On September 20, after a brief artillery bombardment that breached the Aurelian Walls near Porta Pia, Italian troops entered Rome. Papal forces offered limited resistance before surrendering. The event ended the temporal power of the papacy over Rome and allowed the city to become Italy's capital.
Context
By 1870 the Kingdom of Italy, proclaimed nine years earlier under King Victor Emmanuel II, controlled most of the peninsula but still lacked Rome and the surrounding Lazio region, which remained the core of the Papal States. Successive Italian governments had declared Rome the intended capital, yet French troops stationed there since the 1840s and 1860s protected Pope Pius IX and prevented annexation. The outbreak of the Franco-Prussian War in July 1870 forced Napoleon III to withdraw his garrison, removing the principal obstacle to Italian action.
What Happened
In early September, Prime Minister Giovanni Lanza instructed General Raffaele Cadorna to advance into Lazio with roughly 50,000 troops. After occupying Civitavecchia on 16 September, Cadorna sent a final appeal for peaceful surrender to the papal commander, General Hermann Kanzler, who refused. At dawn on 20 September Italian artillery opened fire on the Aurelian Walls near Porta Pia; within a few hours a breach was made. Papal forces, numbering about 13,000 and including Swiss Guards, Palatine Guards, and foreign Zouaves, offered only brief resistance before laying down arms. Casualties were light: 49 Italian and 19 papal soldiers killed.
Aftermath
Pope Pius IX withdrew to the Vatican and declared himself a prisoner, refusing to recognize the loss of temporal power. A plebiscite held on 2 October produced an overwhelming vote for annexation; on 3 February 1871 Rome formally became the capital of the Kingdom of Italy. The Italian government offered the pope sovereignty over the Leonine City and an annual financial settlement, terms the pontiff rejected.
Legacy
The capture of Rome marked the definitive end of the Risorgimento and fixed the political geography of modern Italy. It also inaugurated the “Prisoner in the Vatican” period, during which successive popes remained within Vatican walls until the Lateran Treaty of 1929 created the sovereign Vatican City State. The event accelerated European trends toward secular governance and clarified the separation between spiritual and temporal authority in the Catholic Church.
Why It Matters
The capture finalized the Risorgimento process of Italian unification under the House of Savoy and reduced the pope to spiritual authority only, beginning the 'Prisoner in the Vatican' era. It established modern Italy's political geography and set precedents for church-state relations that influenced European secularization and later Vatican City arrangements.
Related Questions
Why did France stop protecting the pope in 1870?
Napoleon III withdrew his troops to fight Prussia and later lacked the capacity or will to intervene after his defeat at Sedan.
How many soldiers were involved in the capture of Rome?
Approximately 50,000 Italian troops faced about 13,000 papal defenders, most of whom were foreign volunteers.
What happened to the pope after the city fell?
Pius IX retreated inside the Vatican walls and refused to recognize Italian authority, beginning the 'Prisoner in the Vatican' period that lasted until 1929.
When did Rome officially become Italy’s capital?
After a plebiscite in October 1870, the Italian parliament moved to Rome in February 1871.
Did the event involve heavy fighting?
No; the bombardment lasted only a few hours, and casualties totaled fewer than seventy dead on both sides combined.
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Sources
- Capture of Rome, Wikipedia. Accessed 2026-07-04.
- Italian Troops Occupy Rome, Britannica. Accessed 2026-07-04.