Answered by Frank from India | Mar. 31, 2014 20:50
It's still a mystery. It's said that the statues had been ruined during a serious earthquake in 1555. More than 800000 civilians died during this earthquake. The tomb was destroyed too. So were the heads of the statues.
Another popular explanation is that the statues were ruined by the civilians at the end of the Ming Dynasty. One day, a foreigner came to visit the tomb and noticed that the sculptures of his ancestors stood in front of the tomb of the Tang Emperor. He thought it was a humiliation. Then he came up with an idea of ruining the statues. He ruined the civilians' crops at night and told them that it was the statues who came alive and ruined their crops. The civilians asked him how to stop the alive statues. Then he suggested that they should decapitated the statues. The civilians took his suggestion and took away the head of the statues.