The first ruler of a unified Chinese empire and father of the Great Wall, Emperor Shihuangdi commissioned a twenty-square-mile mausoleum, which took around 700,000 laborers more than thirty-five years to complete. Inside, there were about eight thousand terracotta soldiers, seventy burial sites, a zoo, and weapons triggered to go off in case of robbers. The chief craftsmen, it is believed, were also buried there to prevent them from betraying construction secrets.