The battle of Molins del Rey (21 December 1808) was the final battle during General St. Cyr’s campaign to raise the siege of Barcelona. Having defeated the Spanish army under General Vives at Cardadeu on 16 December 1808, St. Cyr had entered Barcelona on 17 December, but his position was not yet entirely secure. Vives had only taken part of his force to Cardadeu, leaving the larger part in the lines around Barcelona under the command of General Caldagues. On the evening of 16 December Caldagues abandoned the siege lines close to Barcelona, and took up a new position on the western bank of the Llobregat River, re-occupying a line of defences that had been constructed at an earlier stage in the siege. He was soon joined by General Reding with 3,000-4,000 survivors from Cardadeu, giving the Spanish 14,000-15,000 men. This was potentially a strong position, but the Spanish did not have enough men to defend it against St. Cyr.
Reding and Caldagues were both in favour of retreating to the mountains on the western edge of the valley of the Llobregat, where they could defend the pass of Ordal, but they had to consult with Vives, who had been rescued from the coast after escaping from Cardadeu. He had given them qualified permission to move, if they could not defend the line of the Llobregat, but this only arrived on the night of 20-21 December. Reding then decided to defend the river, but in any case the French attacked before he would have had a chance to move.
St. Cyr attacked at 5am on the morning of 21 December, with four of the five divisions at his disposal. The first attack was made by Chabran’s 4,000 strong division, against the Spanish left wing at Molins del Rey. Reding responded by moving troops from his right to reinforce his left to deal with this diversionary attack. An hour after the first attack, St. Cyr launched his remaining three divisions against the weakened Spanish right. One of those divisions (Chabot’s) managed to get behind the Spanish army. One by one the Spanish regiments abandoned their positions as the French appeared behind them and to their right, retreating north towards Molins del Rey.
This was the moment at which Chabran should have launched a full scale assault on the Spanish left. If he had done so, then there was a chance that the entire Spanish army would have been captured, but Chabran delayed his attack until most of the Spanish army had escaped. As it was the French captured 1,200 prisoners, 25 guns, three million cartridges and thousands of muskets. These were essential supplies, for St. Cyr had left behind his artillery and much of his ammunition earlier in the campaign.