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.
At first, he planned to organise a resistance in Capua. However, after that city 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.
Gaeta was one of the strongest military fortresses in Europe. 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 cliff was connected to the mainland by a 600 m wide isthmus. Called Montesecco ("Dry Mountain"), the isthmus was the only way for a besieger to conquer the stronghold. The ships of the time were indeed considered too fragile to face the massive fortifications that encircled the promontory. Built in the time of emperor Charles V, the promontory was provided with 220 guns divided between 19 batteries. An additional 230 guns defended the fortress on the mainland side, making a total of 450 cannons, 26 of which were short range mortars. Most of the guns were smoothbore arms, some dating back to the 18th century, and therefore rather imprecise. The massive castle, which commanded the east side on the sea, dated from the time of Emperor Frederick II but was continuously updated. The forces amounted to 19,700 sub-officers and soldiers and 1,770 officers; there were also 3,000 citizens of Gaeta. 17 ships of various nations (including Spain and France) kept open communications with the sea.
The Piedmontese forces were composed of the IV Army Corps, led by general Enrico Cialdini. His staff included the engineer general Luigi Federico Menabrea, future prime minister of Italy. Troops were composed of 808 officers and 15,500 sub-officers and soldiers, supported by 78 modern rifled guns, 65 mortars and 34 smoothbore guns. The most modern rifled ordnance could fire from a distance up to five kilometers without risking any harm from the aged guns of the defenders. The Piedmontese fleet, under admiral Carlo di Persano, had ten ships.
The commander of the fortress of Gaeta was Francesco Millon, a Neapolitan general, who on November 10 was replaced by Pietro Carlo Maria Vial de Maton, an 83-year-old native of Nice. The actual command, however, was placed into the hands of the Swiss Baron General
Felix von Schumacher from Lucerne, aide-de-camp and fatherly friend of King Francis II and Queen Marie Sophie. He was assisted by the Swiss Generals August de Riedmatten and Josef Sigrist. The former was responsible for the seaside front, the latter for the mainland front. But instead of Josef Sigrist it was the Neapolitan Baron Colonel
Gabriele Ussani who commanded this part. The engineering arm was led by the Neapolitan Count General
Francesco Traversa. General Schumacher's aide-de-camp was Alphons Pfyffer von Altishofen who later became the Chief of General Staff of the Swiss army and the initiator and commander of the Swiss fort guarding the Gotthard Pass and rail tunnel. A painting by the German history painter
Karl Theodor Piloty shows him and General Schumacher with Queen Marie Sophie on the ramparts of Gaeta. (Pfyffer also built the Belle Epoque National Grand Hotel in Lucerne and employed and promoted Cesar Ritz, of whom the Prince of Wales said, "He is the king of the hoteliers and the hotelier of the kings".)
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. Since then four Swiss regiments had formed the back-bone of the Neapolitan army until 1859. His son had entered the service in the 1st regiment in 1833 and soon became the personal aide-de-camp of Ferdinand II who commissioned him to weaponize the Neapolitan army.