No one is sure exactly how long the great wall of china is. Many say that the great wall extends some 3, 700 miles ( 6, 000 kilometers) . But, of course, the great wall is not actually a single wall but a series of disconnected walls. snaking along the hills in the southern part of the mognolian plain , the great walk were bulit over centuries, beginning as early as 500 BC. During the Qin Dynasty ( 221-206 BC) many walls were joined and re- enforced for greater strength. In places, the massive walls are as talk as 29.5 feet ( 9 meters ) .