Introduction to the city wall: The outer skin of the city wall of the Badaling Great Wall is made of large city bricks or granite strips weighing more than 2,000 kilograms, with rammed earth and gravel inside, which is particularly strong and neat. The average height of the wall is 7.8 meters, the base of the wall is 6.4 meters thick, and the top of the wall is 5.8 meters wide. It can accommodate five horses and ten people riding together. There are battlements and crenels 1.7 to 2 meters high on the outside of the top of the wall. A small hole is opened on the lower side of the crenellations, called a shooting hole, for archery. At the same time, there is a parapet wall built on the inside of the top of the wall, commonly known as a parapet, which plays a safety role.