Sections of the wall were added and rebuilt by successive dynasties to protect their empires from marauding tribes from the north. The present structure is largely thanks to a 200-year renovation effort during the Ming dynasty of the 14th century. Since then, the wall has zigzagged its way 6400km east to west to the north of Beijing, as far as the mountains of Korea in the east and the Gobi desert in the west. Think of the distance as equalling that between Miami and the North Pole.

The Ming builders were possessed of some pretty dramatic engineering skills, having mastered the art of brick-making at a time when European builders were toiling with cut stone. These builders also managed to place their high-quality bricks in the world's most challenging terrain. In places, the wall rises out of 70-degree slopes.

Not only a deterrent to northern invaders, down the years the wall also became a vital communications route. Messages could be sent from one end of the enormous Chinese empire to the other at incredible speeds, thanks to the beacon towers that had been built every 15 to 30 miles. By day, troops used smoke signals, and by night torches.

Today, the only attacks you are likely to encounter are those of other tourists asking you to take a photograph, or hawkers trying to tempt you with a copy of Mao's Little Red Book.

Badaling is the most well known and best restored section of the wall. It also has the Great Wall Museum and Theatre.