why is Verdun important to French?

Hi! I need the answer for this. During the WW1 france highly defended Verdun from german attacks and I dont know the reason aside from the germans would be able to infiltrate france if they don't and would cause ghe collapse of french morale. Falkenhayn also knew that french will never give up verdun as it has something to do with Verdun being a national treasure. Please enlighten me. Thanks