His first major military action was on May 9, 1849, led him to fight against the troops of Giuseppe Garibaldi in front of Palestrina during the creation of the Roman Republic.

Lanza was field marshal by then, delegated by King Francesco II of the Two Sicilies, to defend the vice-royal capital of Palermo during Giuseppe Garibaldi's Expedition of the Thousand.

He was consequently found completely unprepared at the time of the siege that the Thousand and Sicilian picciotti brought across the Ponte dell'Ammiraglio over the Oreto river and the Termini Gate.

Lanza, reiterating his strategy back in the Sicilian Rebellion 11 years ago, as he had repeatedly announced for the remaining artillery and navy to bombard the city, causing the death of about 600 people and the destruction of a large number of homes.

[1][3] The population of Palermo, including the clergy and nobility of the island, completely abandoned any semblance of loyalty to the Bourbon Monarchy and its army and started a riot after the bombardment of innocent civilians.