https://www.vice.com/en_us/article/n7e5mb/mysterious-section-of-the-great-wall-of-china-isnt-what-we-thought-study-reveals

A mysterious section of the Great Wall of China has unveiled some of its secrets thanks to a years-long intensive survey. As it turns out, the new research raises more questions than it answers.

A team of archaeologists at the Hebrew University of Jerusalem in Israel and the National University of Mongolia have studied a 405-kilometer long wall in Eastern Mongolia called the Mongolian Arc—a portion of the Great Wall with a history and purpose that, until now, were largely unknown.