China's most iconic attraction, The Great Wall of China, was built over 2,000 years ago by Qin Shi Huangdi, the first emperor of China during the Qin Dynasty (221 B.C - 206 B.C.). It is the longest man-made structure in the world with the main wall being around 2,145 miles long with an extra 1,770 miles of branches and spurs.
The wall was originally conceived as a way of protecting various empires from attack from the northern hordes, but because the Great Wall was discontinuous, the Mongol invaders led by Genghis Khan had no problem going around the wall and they subsequently conquered most of northern China between A.D. 1211 and 1223. They ruled all of China until 1368 when the Ming dynasty defeated the Mongols. The wall has been added to at various stages of its history, most famously by the Ming dynasty (1368-1644) following their defeat of the Mongols.
It is the remnants of the stone and brick walls predominately from the Ming dynasty upgrade that survive today. The most visited section of the Great Wall is in Badaling, close to Beijing. It was the first section of the wall to open to tourists in 1957 and is where President Nixon visited and was the finish site to one of the cycling events in the 2008 Summer Olympics. Badaling can get very crowded and there are lots of hawkers so we generally recommend heading further out of Beijing to the much quieter Jinshanling section of the wall.