One of the first projects which the young king accomplished while he was alive was the construction of his own tomb. In 215 BC Qin Shi Huang ordered General Meng Tian to begin its construction with the assistance of 300,000 men. Other sources suggest that he ordered 720,000 unpaid laborers to build his tomb according to his specifications. Again, given John Man's observation regarding populations at the time (see paragraph above), these historical estimates are debatable. The main tomb (located at ) containing the emperor has yet to be opened and there is evidence suggesting that it remains relatively intact. Sima Qian's description of the tomb includes replicas of palaces and scenic towers, "rare utensils and wonderful objects", 100 rivers made with mercury, representations of "the heavenly bodies", and crossbows rigged to shoot anyone who tried to break in. The tomb was built at the foot of Mount Li, 30 kilometers away from Xi'an. Modern archaeologists have located the tomb, and have inserted probes deep into it. The probes revealed abnormally high quantities of mercury, some 100 times the naturally occurring rate, suggesting that some parts of the legend are credible. Secrets were maintained, as most of the workmen who built the tomb were killed.