Built 650 years ago in the Ming Dynasty, the old city wall of Xian was added on the Tang Dynasty walls. Being the most prominent walls built after medieval time, it is also the best-kept and biggest city walls in China. The height of the wall is around 12 meters with watchtowers rising up to above 20 meters. It is a good reference to study the old city plan, history, military and arts of construction in the dynasties.