A Short History of the Chinese Terracotta Army

The first Emperor of China, Qin Shi Huangdi, who died in 210BC, wanted
to be very sure that he would not be disturbed in his final resting
place. He had plans made to position booby traps all around his vast
burial mound at Mount Li in the North West region of China.
The Chinese historian, Sima Qian, who held the position of Prefect of
the Grand Scribes of the Han Dynasty, wrote a huge volume which covered
2000 years of Chinese history.
With regard to the death of Qin Shi, he
noted that the Emperor had ordered a line of loaded hair-triggered
crossbows to be arranged in the passage ways that lead to his tomb and
in concealed places around the outside of it. (As a historical source
this is not solid evidence because the historian did not start writing
until a hundred years after Qin Shi Huangdi died.)
According to Sima Qian, the tomb held great riches so there was quite a
lot to protect. The tomb itself took a labor force of almost three
quarters of a million men thirty six years to complete. To protect the
secret of exactly what valuables had been buried with the Emperor, the
workers who knew what had been carried into the tomb were buried alive,
to make sure that their secrets died with them.