On 20 September 1870, in what came to be known as the Breach of Porta Pia, triumphant Italian Bersaglieri led by Raffaele Cadorna marched down Via Pia, having defeated Pope Pius IX's papal troops.

Rome subsequently assumed the Italian capital city status from Florence, and Via Pia was renamed Via XX Settembre. 140 years after the unification of Italy, the anniversary is celebrated with a three-day programme of events including conferences, exhibitions, concerts, plays and screenings.

Central to the celebrations are the symbolic fortified gates at Porta Pia, which features in a light show as part of the celebrations. Equally symbolic will be the presence at the ceremonies of Cardinal Tarcisio Bertone, Vatican secretary of state when he visits the Museo dei Bersaglieri alongside president of Italy Giorgio Napolitano and mayor of Rome Gianni Alemanno at 10.00 on 20 September. This is the first time that the Vatican has joined the Italian state in a ceremony that marks the defeat of the papacy