Émile Driant was the first high-ranking casualty in the largest  and longest battle of the First World War on the Western Front between the German and French armies, fought when?
Émile Driant Émile Augustin Cyprien Driant (11 September 1855 – 22 February 1916) was a French writer, politician, and army officer. He was the first high-ranking casualty of the Battle of Verdun during World War I.
Plan XVII Plan XVII (] ) was the name of a "scheme of mobilization and concentration" that was adopted by the French "Conseil Supérieur de la Guerre" (the peacetime title of the French General Staff) from 1912–1914, to be put into effect by the French Army in the event of war between France and Germany. Though it was not "a prescribed narrative for the campaign" or battle plan, the deployment made possible a prompt invasion of Germany and/or Belgium before Germany could mobilise its reserves, simultaneous to a Russian invasion of East Prussia. The plan was implemented from 7 August 1914, with disastrous consequences for the French, who were defeated in the Battle of the Frontiers (7 August – 13 September) at a cost of 329,000 casualties. The French northern armies were forced into a retreat as far as the Marne river, where in the First Battle of the Marne (5–12 September), the German armies were defeated and forced back to the Aisne river.