By late November 1808, Napoleon's Grande Armee had shattered both wings of Spain's popular army. To complete his reconquest, the Emperor advanced on Madrid with 40,000 men. General Benito de San Juan assembled a patchwork force of about 9,000 troops -- militia, reservists, and battered regulars -- to hold the heights of Somosierra, the mountain pass shielding the capital from direct French attack through the Sierra de Guadarrama. San Juan placed sixteen cannons in four batteries along the twisting pass, exploiting the terrain to maximum advantage. Two days earlier, Spanish troops at nearby Sepulveda had repulsed an attack by the Middle Guard before being forced to withdraw when their cavalry was defeated by General Lasalle's horsemen. The terrain and Spanish tenacity had shown they could slow Napoleon -- if not stop him.

Napoleon's infantry advanced directly into the pass on November 30, exchanging musket volleys and making slow progress toward the Spanish guns. Impatient and unable to easily outflank the defenders with infantry, Napoleon ordered his Polish Chevau-legers escort squadron to charge the batteries. Jan Kozietulski, commanding the 3rd Squadron, called out Lekka jazda klusem -- light cavalry at the trot -- and led 125 men across a small bridge and into the kill zone. Some historians believe Napoleon only ordered the first battery taken, and that Kozietulski misunderstood. Once under fire from the second battery, however, the horsemen had no choice but to press forward -- slowing down meant certain death. Kozietulski lost his horse at the first battery. Lieutenant Andrzej Niegolewski, returning from reconnaissance, joined the charge. Dziewanowski took command and fell at the third battery, replaced by Piotr Krasinski. Niegolewski led the final push to the fourth battery and somehow survived -- nine bayonet wounds and two carbine shots to the head.

The Spanish artillerymen fought to the death rather than abandon their guns. But the militia defending the slopes between the batteries could not see clearly through the powder smoke. What they saw -- or thought they saw -- was cavalry taking the artillery positions with apparent ease. In reality, only a handful of Poles reached the fourth battery alive. But the illusion was enough. The irregular troops abandoned their positions, triggering a cascade of retreats that collapsed the entire defensive line. When Napoleon saw the fourth battery fall, he committed his Chasseurs of the Guard and Tomasz Lubienski's 1st Polish squadron to drive the remaining Spaniards from the pass. The road to Madrid was open. San Juan raced his surviving forces back toward the capital, where he would later be killed by his own men.

Madrid fell on December 4, after a brief and futile defense by 2,500 regulars and 20,000 civilians. In his official bulletins, Napoleon placed all emphasis on the Polish charge, though the victory at Somosierra was actually the result of combined infantry and cavalry action, with the infantry bearing the heavier fighting. Who led the charge became a matter of fierce dispute. The 13th Bulletin credited General Montbrun, who later laughed at the claim. Major Philippe de Segur wrote that he had commanded it, but both French and Polish sources denied his role. The Poles knew who had bled on that mountainside. Today, the Battle of Somosierra is inscribed on the Tomb of the Unknown Soldier in Warsaw. In Spain, the pass itself remains much as it was -- a narrow corridor through mountain terrain where, for a few chaotic minutes, a small group of horsemen rewrote the campaign.