The Great Wall of China is one of the greatest construction projects in the history of human civilization. The initial construction started more than two thousand years ago during the Spring and Autumn Period and the Warring States Period (770 to 221 BCE), before different sections were connected after the Qin Dynasty unified China. There were large scale expansions of the Great Wall during the Han and Ming dynasties. It is considered a world wonder due to the complexity of the construction and its majestic scale.

Note: The above information is from “Welcome to China” and  only for reference.