The Great Wall started as earth works thrown up for protection by different States. The
individual sections weren't connected until the Qin dynasty (221-206 B.C.). Qin
Shihuangdi, First Emperor of Qin began conscripting peasants, enemies, and anyone else who
wasn't tied to the land to go to work on the wall. He garrisoned armies at the Wall to
stand guard over the workers as well as to defend the northern boundaries. The tradition
lasted for centuries. Each dynasty added to the height, breadth, length, and elaborated
the design mostly through forced labor. It was during the Ming dynasty (1368-1644) that
the Wall took on its present form.
Throughout the centuries, armies were garrisoned along the length of the Wall to provide
early warning of invasion and a first line of defense. The Wall had served well. Only when
a dynasty had weakened from within were invaders from the north able to advance and
conquer. Both the Mongols (Yuan Dynasty, 1271-1368) and the Manchurians (Qing
Dynasty,1644-1911) were able take power, not because of weakness in the Wall but because
of weakness in the government and the poverty of the people.
Over the past few centuries, the Great Wall has served as a source of building materials
for local farms and villages. Aerial photos show that in sections, only the top
battlements show -- the center of the wall has filled with sand and silt.