The siege of Mantua (4 June-30 July 1796 and 24 August 1796-2 February 1797) was the focal point of the third phase of Napoleon's campaign in Italy in 1796-97. During the eight month long siege the Austrians made four separate attempts to relief Mantua, each of which ended in failure, although the siege was briefly lifted twice.
In 1796 Mantua was concentrated inside a bend in the Mincio River, surrounded on three sides (west, north and east) by narrow lakes. The southern approaches were protected by an area of swamps and a canal. The city also had an impressive ring of fortifications, while both bridges across the river were protected by outlying fortifications – the citadel to the north and at San Giorgio to the north east. At the start of the siege the city was defended by 15,000 men, under the command of General Joseph Count Canto d'Yrles, and contained about three months worth of food.
French troops first reached Mantua on 4 June 1796, but General Sérurier, who was given command of the siege, didn't have enough men to conduct a formal siege of the city. Instead he imposed a blockade on the city, and began to prepare for a bombardment. This finally began on 18 July and by the end of the month more than 12,000 explosive shells had been fired into the city. By the end of July the French may have been planning an assault on the city, but a series of Austrian attempts to break the siege meant that no assault would be made.
The first break in the siege came during Field Marshal Würmser's first, and most successful, attempt to raise the siege. When General Quosdanovich emerged from the mountains and captured Brescia, Napoleon realised that his communications with Milan were threatened, and decided to concentrate his entire army at the southern end of Lake Garda, from where he could defeat each Austrian column in turn. General Sérurier was ordered to raise the siege, and on the morning of 1 August the French were gone.
On the following day Würmser reached the city, but this gesture doomed his campaign to failure. Napoleon was able to defeat Quosdanovich in two battles at Lonato (31 July and 3 August), ending any chance that the two Austrian armies could join up. He was then free to defeat Würmser at Castiglione (5 August), and within a few days the siege was re-established. This short break played a part in preventing the French from assaulting the city, for while they were away from their trenches the defenders of Mantua seized their siege guns, and destroyed as many of the siege works as possible.
The second break in the siege was much shorter. Würmser's second attempt to raise the siege went disastrously wrong. His army was defeated and split in two at Bassano (8 September), and Würmser was forced to attempt to escape to Mantua. On 13 September his army arrived outside the city, but with the French in hot pursuit. A two day long battle followed (San Giorgio, 14-15 September), at the end of which Würmser was forced to take refuge inside the city.
From 15 September onwards the French blockaded the city. Supplies ran short, although with 30,000 men at his disposal Würmser was able to send out foraging parties. Disease began to weaken his troops, with 4,000 men dying in the hospitals in six weeks. The Austrians made two more attempts to lift the siege. During the fourth and final attempt, in January 1797, General Provera managed to reach La Favorita, just to the north of the city, where on 14 January he was forced to surrender.
This sealed the fate of Mantua. Food was now running out, thousands were sick, and it was clear that no help could now be expected. On 2 February Mantua surrendered to General Sérurier. Würmser was allowed to return to Austria (although the Directory had wanted him executed as a Frenchman fighting against the country). The surviving members of the garrison were released on parole, on condition that they didn't serve against France for the next year. By the time this period expired, Napoleon had already advanced into Austria and forced the Emperor Francis II to agree to peace.