Before the French, under General Merlin´s command, were forced to abandon Bilbao, they withdrew to the villages of Zornoza and Durango. Here Merlin was reinforced, bringing his total force up to 10,000. He felt that he was now strong enough to offer battle, and so took up a strong position in front of Durango.

Blake, Having seized Bilbao, then decided to attack the French at Durango, with the aim of reaching the “real” road at Bergara, that was the main line of communication between France and the French armies on the Ebro, and its capture earlier in this autumn might have derailed Napoleon’s entire plan. Unfortunately Blake, in common with the entire Spanish high command, had greatly underestimated the strength of the French armies in the area. The successful completion of his plan would probably only have exposed his army to a crushing defeat at the hands of the huge French armies gathering in preparation for the arrival of the Emperor.

Blake’s advance towards Durango also exposed his right flank to an attack from the French forces in the upper Ebro, so he was forced to leave 12,500 men to guard the passes from the Ebro towards Bilbao. This left him 18,000 men. He then further weakened his own position by delaying his advance for nearly two weeks, only leaving Bilbao on 24 October.

This allowed the French to replace Merlin at Durango. On 18 October Marshal Lefebvre arrived at the head of two divisions from his own 4th Corps. He was soon reinforced by one division from Marshal Victor’s 1st Corps. The remaining two divisions from Victor’s Corps took up a position at Murguia, twenty miles to the south of Bilbao. The French now had 35,000 men in a position to trap Blake. King Joseph wanted to spring the trap by having Victor advance towards Bilbao. Victor’s 14,000 men were opposed by around 12,500 Spanish troops, but they were split into two divisions which could have been defeated in detail. If Victor moved quickly enough, Blake would have been trapped between two French armies.

This plan was vetoed by Bessières, Victor and Ney. They were aware that Napoleon was on his way, and had a grand plan of his own, and were unwilling to do anything that might disrupt it. Napoleon’s own plan was for a much more ambitious double-envelopment of the Spanish armies, which would have much easier to achieve if Blake remained in his vulnerable forward position.

Napoleon’s plan was disrupted by Marshal Lefebvre. He had spent a week observing the Spanish army, and had concluded that Blake was vulnerable to attack. The two armies were not dramatically different in size - Blake now had 19,000 men, while Lefebvre had 21,000, but the French army was generally of a higher quality than Blake’s, and so Lefebvre was confident of victory.

The Spanish army was drawn up in three lines in front of Zornoza. The front line was made up of the “Vanguard Brigade” and the 1st Division of Galicia, and was placed on a range of low hills. The six artillery guns with the army were placed with the vanguard. The second line contained the 3rd and 4th Divisions, with the “Reserve Brigade” in Zornoza itself.

Lefebvre’s plan was for a three-pronged attack on the Spanish position. One division attacked the Spanish right, drove in the front line of Blake’s army, and then threatened to outflank the Spanish position. The other two divisions attacked the Spanish centre and left. The entire Spanish front line soon fell back. The entire army then took up a new position on the heights of San Martin. After a short artillery bombardment, Lefebvre sent ten battalions from Sebastiani’s division to attack the new Spanish centre, which quickly gave way. The Spanish left and right wings were now dangerously isolated, but Blake reacted quickly, ordering a retreat back beyond Bilbao.  

The two intact wings were able to cover the retreat, and Blake’s army was able to retreat in good order. The Spanish lost 300 killed and wounded, and 300 prisoners, while the French only lost 200 men.