A French army under Soult overwhelmed the outnumbered Spanish troops under General Belvedere,[2] opening central Spain, including Madrid, to invasion.

The two divisions of the Army of Extremadura were arrayed on the open plain at Gamonal and, broken by a massive cavalry charge, fled in panic, leaving the invaders to sack Burgos.

[2] Milhaud's division of dragoons rode southward and formed up on the banks of the river, facing the Spanish right, while Lasalle's four regiments of light cavalry composed the French centre.

[2] The only troops that held their line were, to the south, the 4th Battalion of the Walloon Guard, under Colonel Vicente Genaro de Quesada, and to the north, Lieutenant-colonel Juan Díaz Porlier's 1st Regiment of Provincial Grenadiers, which managed to withstand the onslaught and retreat in order.

[5] On entering the city of Burgos, the French army celebrated their victory by sacking it and even the house next to that in which Napoleon had taken up his quarters for the night was pillaged and set on fire, so that he had to shift into another street.

The Spanish defeats at Gamonal and Espinosa de los Monteros led to the dispersion of some 20,000 regular troops throughout Cantabria, Castilla-León, Navarra, País Vasco and Rioja, many of whom would form guerrilla bands to fight against the French.