Hi,Mr.QA
The Great Wall runs about 4,500 miles (7,300km) east to west from Shanhaiguan Pass near Bohai (Gulf of Bohai) to Jiayuguan Pass (in Gansu Province). The Great Wall was started to build in the Spring and Autumn Period and the Warring States Period. It has gone through many changes. I bet Badaling Great Wall is not the beginning of the whole project.

Yes, listen to Foster. He knows something about the Great Wall :)