The siege of Rosas was the first engagement during General Gouvion St. Cyr’s campaign in Catalonia in the winter of 1808. The main aim of this campaign was to raise the Spanish siege of Barcelona, which had begun as a loose blockade in August 1808, but which had become increasingly tight as time passed. On 10 August Napoleon had begun to gather a new army at Perpignan to reinforce the weak French garrison of Catalonia, but it had taken a month for the first troops to reach the Spanish border from Italy, while the artillery did not arrive until 28 October. St. Cyr was given a free hand to decide how to conduct his campaign, as long as Barcelona did not fall.
St. Cyr’s first target was the fortress of Rosas, on the coast ten miles inside Spain. There was an excellent harbour at Rosas, which was in constant use by a squadron of British warships conducting a blockade of Barcelona, and St. Cyr was concerned that if he left Rosas in Spanish hands it could be used as a base for attacks on his supply lines. He did not expect the siege to take long. Rosas was a tiny single street town, with a population of only 1,500. It was protected by a strong citadel to the west of the town, and Fort Trinity, overlooking the harbour from the east, but the citadel had been damaged during a previous French siege in 1794 and the breach made then had not been repaired. At the start of the siege the garrison was only 3,000 strong, of whom most were new levies, all under the command of Colonel Peter O’Daly, of the Ultonia regiment. The British contributed one 74 gun ship of the line (first the Excellent and later the Fame), two bomb vessels, and for the last part of the siege the frigate Impérieuse, the flagship of Lord Cochrane.
St. Cyr had 23,000 men at his disposal. He decided to give command of the siege to General Reille, and gave him his own and Pino’s divisions to conduct the actual siege, while the other half of the army guarded against any Spanish attempt to interfere. Reille arrived at Rosas on 6 November, and began the siege on the following day. The first fighting took place on 8 November. The local somatenes (the Catalan militia) took advantage of a dense fog to attack the covering force, while the garrison attacked Reille’s camp. On the same day the civilian population of the town was evacuated by sea.
For the next seven days heavy rain stopped the French from attacking the citadel. One attempt was made to attack Fort Trinity, but without success. Reille summoned his siege artillery, which began to arrive on 16 November. Once the ground was dry enough, he began to construct gun batteries facing the fort and the citadel, and was soon able to open a bombardment. Despite encouragement from Lord Cochrane, O’Daly was increasingly aware that unless a relief force appeared he would have to surrender. The main field army of Catalonia, under the command of General Vives, was engaged in the siege of Barcelona, but the French garrison there was so weak that he could safely have left the militia to conduct the siege while he moved to attack the French around Rosas, but he did nothing. The only attempt to help O’Daly was made by Genral Alvarez, the command of the garrison of Gerona, but that attempt was repulsed at the Fluvia river.
On 26 November the French attacked and captured the weakly defended Spanish positions in the town of Rosas. This allowed them to bombard the previously undamaged eastern side of the front of the citadel, and after two days of bombardment Reille summoned the governor to surrender. O’Daly refused, having on the previous day received the only reinforcements to reach him during the siege (one weak battalion of regulars). In response Reille built a gun battery on the water front, which made it much harder for the British ships to help the Spanish.
By this point Fort Trinity was being defended by a combined British and Spanish garrison, under the command of Lord Cochrane. On 30 November Pino’s division launched another assault on the tower, but without success, and the fort was left alone for the rest of the siege. The French turned their attention to the citadel. Their artillery soon began to open a new breach in the walls. On the night of 3 December O’Daly made his last attempt to length the siege, attacking the most dangerous French gun battery with 500 men, but this attack was repulsed. On the following day the French siege works reached within 200 yards of the wall, and the French began to prepare for an assault, but O’Daly could also see that a defence was hopeless, and on 5 December he surrendered unconditionally. On the morning before the surrender Lord Cochrane had managed to evacuate the garrison of 180 men from Fort Trinity, but the French took 2,366 prisoners from the citadel. The Spanish has suffered around 700 casualties during the fighting, while the French had lost around 1,000 men, and a precious month. The supply situation within Barcelona was becoming desperate.