The Great Wall: the spine of the Chinese people

In exchange for a postcard from Denmark for his daughter’s collection, my Chinese Postcrossing friend sent me one from China. It features the Great Wall, which is probably one of the most well-known symbols of China and of the Chinese people. My friend wrote on the back of the card:

This card shows the Great Wall, we always say that “It is the spine of the whole Chinese people”. Chairman Mao also says: “He who has never been to the Great Wall is not a true man”. So, just find a chance to climb up it!

Although symbols can be easily created and disappear quickly again, the Great Wall has been around for a while. How do you think the Great Wall symbolizes Chinese culture?