Germany attacks the historic French city of Verdun to force France out of the war.
At the end of 1915 German commanders came up with a new plan that they hoped would push France out of the war. They believed if they could defeat France then Britain wouldn't be able to fight on by themselves and Germany would win the war.
The plan was to attack the French city of Verdun. Verdun wasn't a vital city for the French army but it was an important part of French history so they would fight hard for it. Although the city was very well defended, German forces surrounded it on three sides. Germany hoped that France would send all of their available reinforcements to protect Verdun and that they would all be defeated there.
The attack started in February 1916 and it was a very tough fight. With enormous support from artillery fire, the Germans took one of the main fortresses defending Verdun.
For a while it looked as if the German plan was going to work and the French looked like they might crumble. Then a new French commander took over called Henri-Philippe Petain. He told the French army that they wouldn't give up and he encouraged them to keep fighting. This saved the city but the French were still suffering huge numbers of casualties defending it.
Verdun was such a struggle for the French that they needed Britain to launch an attack somewhere else to try to take some German soldiers away from Verdun. This turned in to the Somme Offensive.
The Battle of Verdun was the longest single battle of the First World War. It carried on until December 1916 when the French launched a big attack and the Germans retreated.
Historians disagree over how many soldiers were wounded and killed at Verdun but a reasonable estimate puts the number of casualties at over 700,000, including around 300,000 dead.
French reinforcements rush to Verdun along a vital road called "The Sacred Way".
This area was known as Dead Man Ridge. This is the impact of artillery.
This aerial photograph shows what is left of one of the historic forts that protected Verdun. You can see how many times the area has been targeted by artillery.