"The Great Wall of China is a series of stone and earthen fortifications in China, built, rebuilt, and maintained between the 5th century BC and the 16th century to protect the northern borders of the Chinese Empire during the rule of successive dynasties. Several walls, referred to as the Great Wall of China, were built since the 5th century BC. The most famous is the wall built between 200 BC - 220 BC by the first Emperor of China, Qin Shi Huang; little of it remains; it was much farther north than the current wall, which was built during the Min Dynasty." - in: wikipedia.
Badaling, the outpost of Juyongguan and the barrier to defend Beijing, has its name in virtue of it's location in the main artery of traffic that leads everywhere. It's the earliest section to open to the public and the most famous and best-preserved section of the Great Wall.
The Great Wall is one of the Seven Wonders of the World and also an Unesco World Heritage Site.