Shang Heng, 38, an associate researcher at Beijing Archaeological Research Institute, and his colleagues are busy solving the restoration riddle, which seems to require more than deep analysis of ancient records. Some clues are probably hidden in the Great Wall itself and the team is leaving no stone unturned to decode them.

Since June, Shang has led a fresh round of archaeological research along the Jiankou section. The ongoing project covers an area of 2,530 square meters. "The Great Wall is a cultural icon of China and many think they know all about it. Nothing could be further from the truth," he says.

"Archaeological study in recent years has deepened our understanding. The Great Wall is more than just a fortified boundary. It is, in fact, a very complex defense installation, which once included towers, ramparts, castles and other fortifications," Shang explains.