Most of the dynasties after the Qin Dynasty repaired the Great Wall. Among them, the scale of construction of the Great Wall from the Sui Dynasty to the Song Dynasty was very small.
In order to defend Mongolia, the Jin Kingdom once built the Great Wall, which was larger than the Great Walls of all generations from the Qin and Han Dynasties to the Jin Dynasty.
The territory of the Yuan Dynasty spanned Europe and Asia, far north of the Great Wall, and the rulers themselves were originally nomadic people north of the Great Wall. The Great Wall was of little significance to them. However, in order to prevent the resistance of the Han and other ethnic groups and to inspect passing merchants, many dangerous places in the passes were repaired and guarded by troops.
It is indeed a very controversial matter that Marco Polo did not mention the Great Wall. The Great Wall before the Ming Dynasty was not a brick structure, but a civil structure. In addition, most of the Great Wall had been abandoned for a long time during the Yuan Dynasty, leaving some broken walls and ruins.
However, according to Zhang Dehui, a famous minister of the Yuan Dynasty, "On the way north to Mobei, there are the ruins of the Great Wall, which stretches endlessly." Wang Yun wrote: "There is a northern boundary trench ten miles southwest of Hengzhou, which is still Wanran also". It shows that the Great Wall of the Jin Dynasty still retains a lot. If Marco Polo really traveled throughout China, it would be impossible to turn a blind eye.