Great Wall of China

The Wall, best-known today, acquired its final form during the Ming Dynasty between the 14th through 17th centuries AD.

An excerpt from the article 18 facts about Great Wall of China
Due to the fear of invasions by Mongolian tribes, the rulers of the time decided to build a new fortification based on the ancient wall. The wall stretches from the borders of Korea to the Gobi Desert and is 8,851.8 kilometers long.