Verdun, the iconic city of the Great War
Why Verdun? There are several theories. First it was a city located on a salient that the Germans fought to conquer and the French to maintain, until both parties ended up in a stalemate war of attrition.
Secondly Verdun was a military city, the strongest point in France surrounded by a string of powerful forts like Fort Vaux and Fort Douamont.
Thirdly, when General Pétain took command, he installed a system where the French forces rotated through Verdun. They arrived through the Voie Sacrée from Bar-le-Duc. So a great deal of the French soldiers passed through Verdun.