"They shall not pass" was a slogan famously used during which First World War battle?

"They shall not pass" is a slogan used to express determination to defend a position against an enemy. "On ne passe pas" literally means "one does not pass"; this being a common French idiom to express interdiction. It was most famously used during the Battle of Verdun in the First World War by French General Robert Nivelle.

The Battle of Verdun was fought from 21 February to 18 December 1916. It was one of the largest and longest battles of the First World War on the Western Front between the German and French armies. The battle took place on the hills north of Verdun-sur-Meuse in north-eastern France. The German 5th Army attacked the defences of the Région Fortifiée de Verdun (RFV) and those of the French Second Army on the right bank of the Meuse.

The Battle of Verdun lasted for 303 days and became the longest and one of the most costly battles in human history. An estimate in 2000 found a total of 714,231 casualties, 377,231 French and 337,000 German, for an average of 70,000 casualties a month. Other recent estimates increase the number of casualties to 976,000, during the battle, with 1,250,000 suffered at Verdun during the war.