The Dos de Mayo Uprising in May 1808 rendered the French occupation of Spain insecure. Among other units sent to Spain to reinforce the Imperial French units already there were ten veteran battalions under Georges Mouton. Dropping off one brigade at Vitoria, Mouton joined the army of Marshal Jean-Baptiste Bessières and fought at the Battle of Medina de Rioseco on 14 July 1808. Hilaire Benoît Reynaud's brigade with 3,000 men of the 4th Light and 15th Line Infantry Regiments participated in the battle. The troops left at Vitoria were commanded by Rey, a newly minted brigadier. The brigade consisted of the 1st and 2nd Battalions of the 2nd Light and 12th Line Infantry Regiments and one battalion of the "Garde de Paris".