Seemingly fragile, but a mysterious “biological shell” is what helps the Great Wall of China remain unchanged against time.
A recent study published in the journal Science Advances reveals the astonishing “living mortar” technology employed by the Ming Dynasty to construct the Great Wall.
The research team, led by Professor Bo Xiao from the School of Land Science and Technology at China Agricultural University, uncovered this secret by analyzing samples from eight different segments of this wonder.
A section built with living mortar from the Great Wall – (Photo: SCIENCE ADVANCES).
The eight sections of the Great Wall in the study were all constructed between 1368 and 1644 during the Ming Dynasty.
67% of these samples were found to contain biological materials.
By comparing the mechanical strength of the wall sections made with “living mortar” to purely rammed earth segments using mechanical equipment both in the field and in the laboratory, the authors discovered that the segments made with “living mortar” were three times stronger.
Detailed component analysis revealed that this living mortar contains species of cyanobacteria, moss, and lichen.
These were intentionally incorporated into the mortar by workers during the construction process.
After centuries, the growth of these tiny organisms and the substances they secrete, such as polymers, formed an extremely durable biological layer, enhancing the structural stability of these wall segments, making the rammed earth as strong as concrete.
This helps to explain the enormous mystery surrounding the Great Wall’s remarkable durability: Although rammed earth mixed with gravel—the primary material of the Great Wall—is more prone to erosion than stone, it has remained resilient over time.
According to Live Science, although less durable, it is precisely the rammed earth that facilitates the formation of the “biological shell” from living mortar. This layer has become increasingly robust over time, preventing erosion.
Moreover, this technique of making “living mortar” during the Ming Dynasty is a stunning discovery, demonstrating the remarkable development in scientific technology— including seemingly modern concepts like utilizing biological materials—that the Chinese have applied for a long time.
