In September 1860, as the Garibaldine troops were moving towards the capital Naples (see Expedition of the Thousand), the king of Two Sicilies, Francis II, decided to leave the city on the advice of his Prime Minister Liborio Romano.

However, after Capua was lost to the Garibaldines in the aftermath of the battle of the Volturnus (October), he and his wife Marie Sophie took refuge in the strong coastal fortress of Gaeta.

It consisted of a triangle-shaped promontory (Mount Orlando) which stretched for more than one and a half kilometers and rose to 169 m and with almost vertical cliffs on the seaward sides.

The massive castle, which commanded the east side on the sea, dated from the time of Emperor Frederick II but was continuously updated.

The commander of the fortress of Gaeta was Francesco Millon, a Neapolitan general, who on 10 November was replaced by Pietro Carlo Maria Vial de Maton [it], an 83-year-old native of Nice.

The actual command, however, was placed into the hands of the Swiss Baron General Felix von Schumacher [de] from Lucerne, aide-de-camp and fatherly friend of King Francis II and Queen Marie Sophie.

A painting by the German history painter Karl Theodor Piloty shows him and General Schumacher with Queen Marie Sophie on the ramparts of Gaeta.

The Swiss had served the Kingdom of the Two Sicilies since 1734, and it was General Schumacher's father, Head of the Military Department of the Republic of Lucerne, who had renewed the contract in 1825.

The morale of the defenders, however, increased when veteran general Ferdinando Beneventano del Bosco, one of the few charismatic military figures of the Kingdom of Two Sicilies, arrived in Gaeta.

On 8 December, Francis II issued a proclamation to all his subjects, promising new liberties in lieu of the prosecution of the struggle against the invaders, inciting them to guerrilla operations.

In the meantime, epidemic typhus had begun to spread within the walls of Gaeta: Francis' field adjutant was himself struck down and died on 12 December.

On the afternoon of 5 February, a powder depot of the St. Antonio battery was struck by a Piedmontese grenade, destroying an entire quarter of Gaeta causing huge losses among the soldiers and the population.

The first Piedmontese infantry entered Gaeta one day later, exactly when Francis II and his wife consigned themselves to the victors, hailed by the Neapolitans soldiers who had remained faithful until the very end.

General Enrico Cialdini was later created Duke of Gaeta by the King of Italy as a victory title in recognition of his role during the siege.