Great Wall, China

As the largest structure ever built by human civilization the Great Wall of China certainly is a wonder of the world. Over 6,400km long, construction started as early as the 5th century BC and continued until the 1600's when the Qing dynasty took control of China. 

Materials used to construct the wall varied over time, with original segments made of rammed earth and wood, but l 

 ater sections constructed from brick and cut rock. Later segments also exhibit the familiar watchtowers and barracks that were used to store weapons and house soldiers. 

Being constructed over a 2,000 year period, the wall was never a single permanent structure, and in fact maps show that the wall has actually occupied several locations in an effort to keep northern peoples from invading China.