Which battle was the longest single battle of World War I?

Verdun is a small city in the Meuse department in Grand Est in northeastern France. Meuse is named after the river Meuse and Grand Est is an administrative region. Verdun is well known for giving its name to the battle of Verdun of the First World War. One of costiliest battles in military history, Verdun exemplied the policy of a 'war of attrition' pursued by both sides. It was fought from 21 February to 18 December 1916 on the Western Front.

Following the outbreak of war in August 1914, the German army opened the West Front by invading Luxemberg and Belgium, then gaining military control of important industrial regions in France. The battle of Verdun took place on the hills north of Verdun-Sur-Meuse in north-eastern France. The German 5th Army attacked the defences of the fortified region of Verdun and those of the French second army on the right (east) bank of the Meuse.

In 2000, Hannes Heer and K. Naumann calculated that the French suffered 377,231 casualties and the Germans 337,000. In France, the battle came to symbolise the determination of the French Army and destructiveness of the war.