Unraveling the Most Mysterious Section of the Great Wall of China

The Mongolian Arc is a little-known section of the Great Wall of China that stretches for over 405km within eastern Mongolia. Its purpose and importance are unknown. Unlike the more dramatic parts of the Great Wall, few have studied it.

It’s nicknamed the Mongolian Arc because it curves through the landscape, paralleling the border between Mongolia and China. Ancient texts suggest that it was built between the 11th and 13th centuries. The wall and its creation are mentioned in these texts, but the reasons for its construction were not.

A trench runs parallel the wall, and there are 34 structures along it. Again, no one is sure what these were for. The Arc also features wide gaps, suggesting that it may have been built in a hurry and was incomplete.

aerial of square structure

One of the 34 unusual structures along the Mongolian Arc. Photo: Fung et al 2024


A research team recently mapped the wall using GIS (Geographical Information System), remote sensing, satellite images, Chinese atlases, and field studies. They want to analyze the wall further.

Two theories

There are currently two theories about the wall’s purpose. Both incorporate an explanation of the gaping holes in the wall.

The first is that it was built around the time of the Mongol invasion of Jin territories. Historian Wang Guowei came up with this hypothesis back in 1921. It suggested that construction sped up dramatically to defend against invading Mongol armies.

A photo of the wall and trench between structures 17 and 18.

A photo of the wall and trench between structures 17 and 18. Photo: Fung et al 2024


A second theory is that the ancient wall controlled the movement of people and their herds, and may have even made it easier to levy taxes. Perhaps the holes were intentional, acting a bit like gateways.

The 34 structures are not in particularly effective positions. They are not visible to each other and would have been very little help in controlling an invasion.

This study is part of a wider project looking at the ancient walls and structures in eastern Mongolia and northern China.

Map showing the Mongolian Arc (red) alongside the Great Wall of China (green)

Map showing the Mongolian Arc (red) alongside the Great Wall of China (green). Image: Fung et al 2024

Rebecca McPhee

Rebecca McPhee is a freelance writer for ExplorersWeb.

Rebecca has been writing about open water sports, adventure travel, and marine science for three years. Prior to that, Rebecca worked as an Editorial Assistant at Taylor and Francis, and a Wildlife Officer for ORCA.

Based in the UK Rebecca is a science teacher and volunteers for a number of marine charities. She enjoys open water swimming, hiking, diving, and traveling.