Researchers studying China’s largest and probably most famous landmark - the Great Wall - have discovered the remains of over 130 concealed doors dotting this monumental fortification.
These passages were apparently designed for scouts sent on missions beyond the wall, even though they could have also been used for other purposes.
Records from the time of the Ming Dynasty, which reigned in China from 1368 to 1644, suggest that nomadic tribes were sometimes allowed to use these entrances to move their cattle to areas suitable for grazing, according to Chinese media.
"These all help prove that the Great Wall is not completely closed, but 'open' in order," said Zhang Yukun, a professor from Tianjin University and head of the research team.
The hidden doors were designed to be indistinguishable from the outward surface of the wall and could also provide Chinese soldiers stationed there with the means to break out and launch a surprise flanking attack against assaulting enemies from a neighboring section of the fortification.
"This is a great demonstration of ancient China's military wisdom," another member of the research team, Li Zhe, said as quoted by media.