He argues that creating this sort of realistic sculpture is not something that a sculptor could learn without some practice, taking the ancient Greeks centuries to master it.
"The creation of a believable human body preoccupied generations of Greek sculptors. It was a complex artistic and intellectual process that did not happen overnight," Nickel writes.
Why did they stop building the statues?
All this research leaves another mystery in its wake. After the First Emperor's death the rulers that came to power, the Han Dynasty, stopped building life-size sculptures, opting instead for miniature representations of people, animals and objects, Nickel said.
Several reasons could explain why the people stopped building these human-like statues, Nickel said. For instance, the skills involved in building these sculptures were complicated and, by the time Han rulers started building large tombs again, the people who had these skills could simply have died.
But there is another idea, one hinted at by the "heavenly taboo" recorded by Ban Gu that "disaster" happens when foreign models are followed recklessly. To the ancient Chinese, the 12 giant statues clad in foreign robes, and the Terracotta Warriors buried in pits, would have represented something unusual and foreign, Nickel said.