The combat of San Pelayo (24 March 1813) saw the Spanish under Mendizabal attempt to defeat the French forces preparing to besiege Castro-Urdiales, but ended as a costly draw.
Early in 1813 Napoleon placed General Clausel in command of the Army of the North. One of his orders was to recapture the port of Castro-Urdiales, a few miles west of Bilbao, then the only fortified port in Anglo-Spanish hands on that stretch of the coast and a useful base for the Royal Navy. Clausel believed that the port was poorly fortified and could easy be captured. On 21 March he left Bilbao at the head of a force made up of most of General Palombini’s Italian division, and one French battalion, but when he reached the port on the following day it quickly became clear that it would probably need a formal siege. News then arrived that Bilbao was being threatened, so Clausel left with his French battalion.
Palombini was left at Castro-Urdiales, and camped at San Pelayo. There is a hamlet of that name twenty miles to the south. Although that seems a long way from the port, Gabriel de Mendizabal with 3,000-4,000 Spanish troops was in the area, so Palombini may have camped at that distance to avoid an early clash with the Spanish.
If that was the case, then the plan failed. On 24 March Mendizabel attacked the Italian camp. He split his force into several columns and attempted to support Palombini’s position. Palombini sortied from his camp, and forced the Spanish to retreat, although not without suffering fairly heavy losses. Vacani, the chief engineer in the force, claimed that the French lost 110 men killed and wounded, but Martinien’s lists of French casualties shows that the three units present, the 4th , 6th and 2nd Ligeros lost 3 officers and 16 wounded in the fighting, suggesting a total loss of nearer to 350 men.
Soon after this clash, Clausel returned to the front, only to decide that the port was too strong to attack with the forces at his disposal. Palombini was ordered to destroy the goods he had prepared for the siege, and move west to raise the siege of Santona.
A History of the Peninsular War, Volume VI: September 1, 1812 to August 5, 1813: Siege of Burgos, Retreat of Burgos, Vittoria, the Pyrenees