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.
The insurgent army, numbering approximately 100,000,[REF] took up a defensive position at the Bridge of Calderón, where the road from Guanajuato to Guadalajara crossed the Calderón River.