The underground fortress, which featured 400-metre long parrallel galleries linked by four perpendicular galleries that could hold up to 2 000 men. It was therefore used as a shelter (mess, baker's cooperatives and, of course, a hospital) and some members of the local council also exercised their functions from within the galleries.

On 13th September 1916, the President of the French Republic awarded the town the Legion of Honour, the French War Cross and six Allied decorations (Great Britain, Italy, Belgium, Russia, Serbia and Montenegro) in the presence of Generals Joffre, Pétain and Nivelle.

But the Citadel went down in French History on 10th November 1920 when Private Auguste Thin chose the body of the Unknown Soldier - who today rests under the Arc de Triomphe in Paris - from eight coffins representing the various different French battlefields. When making his choice, the private added together the numbers of his regiment (the 132nd) and therefore picked out the sixth coffin.