Spreading from Sandong in the east to Lop Lake in the west across the northern border of China, The Great Wall of China is a UNESCO world heritage site. According to archaeological surveys the wall measures 21,196 km with all its branches and stands across deserts, grass lands, mountains and plateaus. Though the wall is over 2000 years old, the part we see now is built by the Ming Dynasty. Besides controlling the border and allowing imposition of taxes along the silk route, the wall also had much military importance with its troop barracks, and smoke signaling facilities. Millions of tourists visit the wall every year.