Why is Xi 'an City Wall also called the Forbidden City?

The wall of Xi has never been called the Forbidden City. It's boring for you to make up such a lie. There is a saying in Xi 'an that there are pigsty in Qin Brick Han Tomb, which means there are three kinds of historical sites in Xi 'an, namely the wall brick in Qin Dynasty, the ancient tomb in Han Dynasty and the wall built by Qin Wang in Ming Dynasty. The wall of Zhu Jiaxiu is also called pigsty;