The Great Wall is an ancient defense project with the longest construction time and the largest amount of engineering in China. Beginning in the seven or eightth century BC, it has been continuously built for more than 2,000 years, with a total length of more than 50,000 kilometers. It is called "up and down two thousand years, more than 100,000 miles." Such a vast project is not only unique in China but also in the world. Therefore, it was listed as one of the Seven Wonders of the Middle Ages with the Colosseum and the Leaning Tower of Pisa hundreds of years ago.