Almost 100,000 Mexican revolutionists contributed to the attack, commanded by Miguel Hidalgo, Ignacio Allende, Juan Aldama and Mariano Abasolo. The Royalist forces of New Spain, made up of little more than 6,000 professional soldiers, and fighting for the King of Spain, were led by Félix María Calleja del Rey, a Spanish military officer and (later) viceroy of New Spain. He was later given the title of conde de Calderón for the Spanish victory.
The battle owes its name to the adjoining bridge, and the combatants' objective. The Battle of Calderón Bridge was the last militant episode of the first stage of the War of Independence.
Following Hidalgo's failed attempt to take Mexico City in October 1810, insurgent troops retreated toward Guanajuato, pursued by Royalist forces led by General Félix María Calleja. Unable to defend positions at Aculco, where Calleja's army intercepted the insurgents, Hidalgo decided to continue his army's retreat towards Guadalajara.
The insurgent army, numbering approximately 100,000, took up a defensive position at the Bridge of Calderón, where the road from Guanajuato to Guadalajara crossed the Calderón River. Ignacio Allende commanded the troops at the position. Calleja's forces, which numbered only 6,000 but were better equipped than the insurgent forces, arrived at the Bridge on January 16.
As the battle ensued, Royalist artillery struck an insurgent ammunitions wagon, which caused it to explode. The explosion dispersed much of the insurgent force, giving victory to the much smaller but better disciplined and equipped Royalist forces. Insurgent forces fled northwards after losing the battle with Royalist troops following them.