In 1808, the I Corps under Marshal Claude Perrin Victor was transferred to Spain to fight in the Peninsular War. Barrois commanded the 2nd Brigade in Dupont's former division, now led by François Amable Ruffin. He led his brigade with distinction at the Battle of Espinosa de los Monteros on November 10–11, 1808. In this action, Victor recklessly attacked on the first day before all his troops were available and was repulsed. On the second day, the marshal made a more skillful assault and routed the Spanish army. The French lost 1,000 killed and wounded while inflicting 3,000 casualties and capturing six guns and the Spanish wagon train.