The Battle of Ocaña was fought on 19 November 1809 between French forces under Marshal Jean-de-Dieu Soult against the Spanish army under General Juan Carlos de Aréizaga, which suffered its greatest single defeat in the Peninsular War.

General Aréizaga's Spanish army of 51,000 troops lost nearly 19,000 men killed, wounded, prisoners and deserters, mostly due to the French use of their cavalry.

[citation needed] The strategic consequences were also devastating, as it destroyed the only force capable of defending southern Spain.

They called for assistance from Arthur Wellesley, Viscount Wellington, but after experiencing a lack of cooperation from the Spanish during the Talavera campaign the British general refused.

Several days of fruitless countermarching found the thoroughly alerted French concentrated and moving to intercept the Spanish army.

[9] William Napier writes of the cavalry action before the battle: "The Spaniards came on at a trot, and Sebastiani directed Paris, with a regiment of light cavalry and the Polish lancers, to turn and fall upon the right flank of the approaching squadrons, which being executed with great vigor, especially by the Poles, caused considerable confusion, which the Spanish general endeavored to remedy by closing to the assailed flank.

In reserve behind Castejon stood Jacome's men, Zerain supported Giron and Copons backed up Vigodet.

[11] On 19 November, the massed battery pounded the Spanish center as Leval attacked Castejon and Werlé went in against Lacy's division.

Then, as the IV Corps halted to wait for artillery to be brought up, the two Spanish divisions surged forward into musket range and opened fire.

Faced by the threat of infantry pressing their front while cavalry slashed into their flank, the Spanish divisions collapsed one after another and bolted for the rear.

At this crisis, Dessolles and the Royal Guard dashed across the ravine and burst into Ocaña, severing the Spanish left from their disintegrating center and right.