The French responded quickly to the Neapolitan incursion, forcing them to retreat, and then undertook an invasion of the Kingdom of Naples. Plagued by cold and heavy rains, the Neapolitans fell back along the Appian Way. Thousands of troops deserted and many more were captured. Pezza, who was with the rear guard, was almost captured by the French, but escaped by donning peasant dress, and took to the hills above Itri. During the retreat, the Neapolitan "Reggimento di Lucania" fortified an old Roman villa, the "Fortino di San Andrea", located about a mile north of Itri, where a pass carries the Appian Way over the Aurunci Mountains. On 26 December, reinforced by some irregulars hastily recruited by Pezza, the regiment ambushed elements of the French "Polish Legion", touching off a three-day skirmish. Unable to get through the easily defended defile, some French troops passed down the coast road, along the ancient Via Flacca, from Terracina to capture Sperlonga. The weather was foul, very cold with incessant rains that turned to ice. From Sperlonga, the French began working their way overland across the mountains, to outflank the Neapolitans at the old villa, and by dawn on the 29th were in position to attack. But the French movement had been detected by Pezza's irregulars, who were patrolling the hills, and they guided the Neapolitan troops safely out of the encirclement, so that they could fall back on the great fortress of Gaeta, about 15 miles down the coast. The French pressed on, and over the next few weeks, despite unusually cold and icy weather, overran the rest of Naples, capturing the city itself on 22 January 1799 and proclaiming the Parthenopaean Republic. For Pezza, the most critical event of this period occurred on 30 December, when French and Polish troops captured Itri. A band of peasants from the vicinity attempted to resist, but were rapidly overcome. The invaders then shot their prisoners, plundered the town a bit, proclaimed a new age of freedom, erected a "Liberty Tree," and held a ball.