Sedan, Battle of, a decisive French defeat in the Franco-Prussian War (1870–71). Before this battle, France had suffered a series of reverses along its eastern and northeastern frontiers. In August, 1870, one French army was trapped by the Prussians at the fortified city of Metz. A second army, led by Emperor Napoleon III, moved into the town of Sedan on the Meuse River, about 140 miles (225 km) northeast of Paris. There it was encircled by Prussian forces under the personal direction of King (later German Emperor) William I.

In a day-long battle at Sedan on September 1, 1870, Prussian artillery devastated French defenses. French infantry and cavalry suffered heavy losses in unsuccessful attempts to break through the Prussian lines; some 3,000 French troops were killed and 14,000 wounded. The next day, with all hope of victory lost, Napoleon surrendered himself and his army of more than 100,000 men to the Prussian king. The defeat had a profound effect on France; revolution broke out in Paris and within a week the Second Empire was overthrown.