As you first look upon the Great Wall, it is impossible not to be awestruck at this man-made structure. Construction started in the 7th century BC, with additions and rebuilding continuing until the 16th century AD. The Great Wall was built to keep out the warring invaders of the north, but additional sections were extended eastward for nearly 6,700 kilometres. The Badaling section is the most well preserved section of the Wall. You can climb to its top and walk for a mile in either direction: the Great Wall snakes ahead though the mountains as far as you can see.