Qin Shi Huang was king of the small state of Qin by the age of 13. One by one, Qin Shi Huang defeated neighbouring states, swallowed their territory into his growing empire and enslaved and castrated their citizens. "Every time he captured people from another country, he castrated them in order to mark them and made them into slaves," says Hong Kong University's Xun Zhou. "There were lots and lots of eunuchs in his court. He was a ruthless tyrant." But still, no Qin, no China.