By the autumn of 1808, Spain was in open revolt against French occupation. The Dos de Mayo Uprising that May had set the entire peninsula ablaze, and for a brief, astonishing moment, Spanish arms had prevailed. At Bailen in July, a French army had surrendered in the field for the first time in the Napoleonic era. The shock reverberated across Europe. Napoleon himself crossed the Pyrenees to crush the rebellion, bringing the full weight of the Grande Armee to bear on the fractured Spanish forces. Lieutenant General Joaquin Blake commanded the Army of Galicia, one of several Spanish armies attempting to hold the northern front. His forces were positioned near the village of Espinosa de los Monteros, where the steep terrain of the Cantabrian range offered some defensive advantage against Marshal Victor's advancing columns.

On 10 November, Victor launched a series of attacks against Blake's positions. What followed surprised the French. General La Romana's Division of the North, composed of disciplined regulars who had been serving in Denmark before being smuggled back to Spain by the Royal Navy, fought with a tenacity that threw back every assault. By nightfall, Blake's lines held firm, and French casualties mounted. It was, for a moment, a repeat of the stubborn resistance that had characterized Spanish defenses throughout the summer. But Victor was not finished. He spent the night reorganizing his forces for a coordinated assault that would exploit the weaknesses in Blake's extended line.

The morning of 11 November brought a different battle. Victor's renewed attack pierced Blake's left wing and drove the Spanish from their positions. General Acevedo ordered a counterattack with two brigades of Asturian troops, roughly five thousand men each, led by Cayetano Valdes y Flores and Gregorio Bernaldo de Quiros. These were raw recruits, many of whom had never faced combat. Their commanders led from the front, as Spanish officers of the era were expected to do. The brigades charged downhill into a wall of musket fire from Maison's brigade of fusiliers. The result was catastrophic. Quiros was killed outright. Valdes and Acevedo both fell seriously wounded, Acevedo permanently losing his sight. More than five thousand Spanish soldiers became casualties in a single engagement.

Blake gathered what remained of his shattered army and began a heroic retreat westward through the Cantabrian Mountains, pursued by Marshal Soult's forces. The mountain passes that had offered defensive advantages now became corridors of suffering for exhausted, demoralized troops trudging through November cold. When Blake finally reached Leon on 23 November, only 20,000 of his men remained, and those in terrible condition. Napoleon's invasion proceeded to the Battle of Tudela and beyond, sweeping aside Spanish resistance with a methodical brutality that would define the Peninsular War for years to come. The retreat from Espinosa later found its way into literature when C. S. Forester, author of the Horatio Hornblower novels, opened his book The Gun with the Spanish army's desperate flight from the battlefield.

Espinosa de los Monteros sits today much as it did in 1808, a quiet village in the deep valleys of the Cantabrian range. The battle's name is inscribed on the Arc de Triomphe in Paris, one of dozens of Napoleonic victories etched into that monument's stone. For Spain, the engagement represented something more complicated than simple defeat. La Romana's regulars proved on the first day that Spanish troops could fight professional European armies to a standstill. The catastrophic second day showed what happened when untrained volunteers were fed into the same meat grinder. The Peninsular War would grind on for another six years, and Spain's resistance, however costly, would ultimately contribute to Napoleon's downfall. The mountains above Espinosa witnessed both the best and worst of that long struggle.