Aerial photo shows the ruins of the Great Wall built in the Qin (221 BC to 206 BC) and Han (206 BC to 220 AD) dynasties, in Urad Front Banner in Bayannur, north China's Inner Mongolia Autonomous Region, Oct. 16, 2020. (Xinhua/Peng Yuan)

Aerial photo shows the ruins of the Great Wall built in the Qin (221 BC to 206 BC) and Han (206 BC to 220 AD) dynasties, in Urad Front Banner in Bayannur, north China's Inner Mongolia Autonomous Region, Oct. 16, 2020. (Xinhua/Peng Yuan)

Photo shows the ruins of the Great Wall built in the Qin (221 BC to 206 BC) and Han (206 BC to 220 AD) dynasties, in Urad Front Banner in Bayannur, north China's Inner Mongolia Autonomous Region, Oct. 16, 2020. (Xinhua/Peng Yuan)

Aerial photo shows the ruins of the Great Wall built in the Qin (221 BC to 206 BC) and Han (206 BC to 220 AD) dynasties, in Baotou, north China's Inner Mongolia Autonomous Region, Oct. 15, 2020. (Xinhua/Peng Yuan)