Wellington, well done.(battle won by the Duke of Wellington)

Rory Muir Salamanca, 1812. Yale University Press, 322 pages, $35

On the evening of August 16, 1812, the publisher Charles Knight was at his desk attempting to write a "death-song" for a Spanish guerilla when he heard the 29th regiment leave its barracks in Windsor. With band playing, the soldiers marched into central London, and Knight joined the cheering crowd that surrounded them. "I followed the measured tramp of the soldiery, in common with the great mass of our population, unknowing what was to be done, and yet filled with the passionate desire of the hundreds around me to give expression to the belief that the tide had turned--that England might shout for a mighty victory by land, as she had shouted for the Nile and Trafalgar."

It was the night that news reached London of the victory at Salamanca. In the days that followed, bells were rung across the land, a prayer of thanks was read in every church in England and Ireland, and Lord Liverpool's weak government called a snap election to take advantage of its new popularity. Salamanca was Wellington's finest victory, but, if it is remembered today at all, it is always overshadowed by Waterloo, a battle that the French lost far more than the British won.

In 1812, Wellington had already been at war in the Peninsula for four years. That May, he invaded Castile to attack the French "Army of Portugal" under Marshal Marmont. The youngest of Napoleon's marshals, Marmont was a skillful but unlucky commander. (Known by his title Duc de Raguse, his lasting achievement seems to have been to add the word raguser ["to betray"] to the French language, alluding to his betrayal of his friend Napoleon in 1814.)

With armies of just under 50,000 men each, the two began a campaign of flanking movements and retreats. On the morning of July 22, Marmont mistakenly thought that Wellington's army was in retreat and that there was but a single division left as cover. Anxious to maul this rearguard, he sent two of his divisions in a rapid maneuver. The leading one overextended the French left and created a gap between itself and the following division. Wellington recognized a golden opportunity. Two of his infantry divisions engaged and broke the isolated French left and then the heavy dragoons of John Le Marchant crashed into the disordered and confused French infantry and turned them into a fleeing rabble that no commander could hope to rally. In forty-five minutes, the left wing of the French army had simply ceased to exist.

The British attacks on the French middle were initially repulsed, but Wellington's reserves, suffering heavily, broke the French again and the battle became a rout. The French were saved from complete destruction only by darkness and Spanish cowardice. Unknown to Wellington, his Spanish allies had abandoned the fortress at Alba de Tormes and so the French were able to escape across the river. Even so, three days later the "Army of Portugal" could only muster 20,000 troops. It was the worst French defeat since the Annus Horribilis of 1799, and the war that Napoleon thought would cost him 12,000 casualties had become, in his own words, an "ulcer," which cost him 240,000 by the end.

The historian Rory Muir set out simply to retell the story of this landmark battle in detail. This proved surprisingly difficult to do. The primary sources all tell a slightly different story. He discovered that it is next to impossible to know exactly what happened at any moment of the battle. Historians, Mr. Muir points out,