Malplaquet, battle of, a major engagement in the War of the Spanish Succession (see Spanish Succession, War of the). On Sept. 11, 1709, the combined forces of England and the Holy Roman emperor, led by the Duke of Marlborough and Prince Eugene of Savoy met the French army under Marshal Villars. Although the French were forced to retreat, the Anglo-imperial army, attacking strongly fortified positions, suffered more than 20,000 casualties, twice the number of French casualties. The battle was a strategic victory for France as it prevented an allied advance to Paris.