DESC: Modern engineers and some of the world's leading historians puzzle over one of the great engineering mysteries of humankind: The Great Wall of China. Little is known about the actual building of the wall, such as who conceived the project and how it was built, yet some claim that it was a wellspring of madness and death. Visible to the naked eye from space, The Great Wall is one of the seven wonders of the world, and its mystery is thoroughly examined in this engaging and insightful documentary from The History Channel.