The 2000 years old Great Wall of China is one of the biggest constructions on earth, an inmense fortified wall crossing China from east to west of China, crossing 15 provinces, regions and all sorts of natural landscapes. In 1987, it was listed as World Heritage by UNESCO and attracts thousands of visitors every year.

But how long is the Wall? After more than 5 years of research, the Chinese National Office of Historical Relics has come up with a very accurate measurement: 21196.18 km.

However, the research has also highlighted the erosion due to the passing of time and the expoliation of tourists who take pieces of stones with them.