Victor's objective was straightforward: destroy the Army of Extremadura and open the road south. Cuesta had been retreating before the French advance, but on March 27, reinforced by 7,000 fresh troops, he decided to stand and fight. The battlefield southeast of Medellin was bounded by the Guadiana River to the north and the Hortiga River to the east, terrain that channeled both armies into a confined space. Victor had 17,500 troops against Cuesta's 23,000, a significant numerical disadvantage. But Victor held a 50-to-30 advantage in artillery pieces and fielded 4,500 cavalry against Cuesta's 3,000. More importantly, he had a plan -- and a reserve.

The French deployment was unusual and deliberate. Victor placed an infantry division under General Villatte in the center, anchoring the main road from Medellin to Don Benito. His two wings -- cavalry divisions reinforced with German infantry from the Confederation of the Rhine, commanded by the brilliant Lasalle on the left and Latour-Maubourg on the right -- were positioned far forward and to the sides. Behind them, an infantry division under General Ruffin waited in reserve. The intention was counterintuitive: let the Spanish push the wings back, drawing Cuesta's extended line deeper into a narrowing pocket, until the wings could snap inward with support from the center. Cuesta, who committed every man he had to the initial assault and kept no reserves, played directly into the trap.

The cannonade began around 1 p.m., and Cuesta's forces initially performed well, driving back both French wings and repelling an early cavalry charge on the left. Lasalle's position grew precarious as the Guadiana at his back left barely a mile of retreat. But by mid-afternoon, both French flanks had withdrawn into easy supporting distance of Villatte's center. When Latour-Maubourg ordered a second cavalry charge, his dragoons broke three Spanish cavalry regiments, who fled and left their infantry exposed. Without reserves to plug the gap, Cuesta's line crumbled from the west. Lasalle, seeing the rout, launched his own counterattack with fresh battalions from Villatte -- hussars and chasseurs smashing through the eastern flank while dragoons rolled over the Spanish center. The Spanish army tried to flee in every direction, but a large portion of the right flank found itself completely encircled.

What followed exceeded the norms even of Napoleonic warfare. French soldiers gave no quarter to Spanish troops, whether standing or surrendering. Entire units were annihilated where they stood, and prisoners taken during the pursuit were killed. The field was strewn with Spanish dead across enormous stretches of ground. Estimates of Spanish casualties vary, but French burial details recorded interring 16,002 bodies in the days that followed. Some historians estimate total Spanish killed at around 8,000, with 2,000 captured; others accept the burial count at face value. The French suffered roughly 1,000 casualties. Cuesta himself barely escaped with his life. The Spanish also lost 20 of their 30 artillery pieces, leaving the Army of Extremadura shattered as a fighting force.

The Battle of Medellin opened southern Spain to French occupation, a process completed later that year with the victory at Ocana. The engagement is inscribed on the Arc de Triomphe in Paris, one of the battles Napoleon considered worthy of memorializing. For Cuesta, it was a catastrophe from which his reputation never recovered, though he would fight again alongside Wellington at the Battle of Talavera four months later. For the people of Extremadura, the battle left a landscape scarred by mass graves along the Guadiana -- a reminder that the Peninsular War's costs were measured not just in territory lost but in the lives of thousands of Spanish soldiers whose commanders failed them.