Hidden near the border of Shanxi and Inner Mongolia, the Zhenchuankou Great Wall (镇川口长城)—also known as the Zhenchuan Pass Great Wall (Literally Control Mountains Pass), part of Datong Great Wall constructed in Ming Dynasty (1368-1644) — once guarded a vulnerable stretch of China’s northern frontier. Built during the Ming Dynasty, this section saw frequent attacks, and many watchtowers were added to strengthen its defenses.