Anyone who has seen pictures from World War I is familiar with the scenes of muddy trenches, where soldiers spent a good part of their time hiding from enemy gun fire and shells. But deep underneath them, in tunnels up to 100 feet underground, their fellow soldiers were fighting a different war.

From the BBC:

Archaeologists are beginning the most detailed ever study of a Western Front battlefield, an untouched site where 28 British tunnellers lie entombed after dying during brutal underground warfare. For WWI historians, it's the "holy grail".

The Somme region of France was one of the most deadly places in France during World War I. Almost every week, farmers in the Somme turn up what they term "the iron harvest." Pieces of bullets, grenades, mortars. And about a dozen times a year they pull up a body of some unidentified soldier, lying long dead in a collapsed trench or unmarked grave.