One sector of the Battle of Verdun ...
https://www.youtube.com/watch?v=KzDs76dYSO4The before and after photos of Fort Douaumont are quite interesting in that there was not much remaining of the place after so many shells pounded it for around ten months.
There are remains of 125,000 French and Germans at the ossuary near the fort, and another 15,000 in the cemetery.