History
The Great Wall, as we know it, is actually a series of several walls built at different times by different emperors.
Second Great Wall . built by the Han Dynasty 205-127 BC
Third Great Wall . built by the Jin Dynasty 1200 AD
Fourth Great Wall .built by the Ming Dynasty 1367-1644

The First Great Wall was ordered built in 214. BC by Qin Shi Huangdi after he had finished consolidating his rule and creating a unified China for the first time. The wall was designed to stop raids by the Xiongnu raiders from the north. 500,000 laborers were used during the 32 year building period to create the First Great Wall.
The Wall, unplugged

Considering that it was constructed for the purpose of keeping foreigners out of China, it's ironic that the Great Wall has become China's number one attraction for visitors from abroad. If you've only done the chairlift at Badaling, however, you can hardly count yourself as a Wall veteran. Indeed, speak to any tourist visiting Beijing, and you may well get the impression that there are only three parts of the Great Wall to be seen in the country. Backpackers are especially quick to make fun of the Badaling and Mutianyu crowd, and speak in hushed tones of the "real" wall at Simatai.
Let's be honest - all three of these sections are intensely marketed to tourists of varying persuasions - and while all of them are fine parts of the Wall to see, on a monument with sections scattered across the country there is certainly a lot more ground to be covered.
We may no longer be able to follow in the steps of William Lindesay - the Briton who journeyed the entire length of the Wall on foot in 1987 - but there are still numerous locations within reach of Beijing where visitors can enjoy features and designs unique to each particular section.