Emperor Gaozong of Tang Dynasty and Empress Wu Zetian were buried together in Qianling Mausoleum. With grand scale and magnificent momentum, Qianling Mausoleum is the most representative one in Tang imperial tombs. Outside the Zhuque Gate of the tomb, there are 61 stone human statues. These statues are as large as real people. However, the heads of these 61 stone statues have all disappeared. So, why were these stone human headstatues destroyed? It has been an unsolved mystery for more than 1000 years.