History of Terracotta Army
The construction of the tomb was described by historian Sima Qian (145–90 BCE) in his most noted work Shiji, written a century after the mausoleum’s completion. Work on the mausoleum began in 246 BCE soon after Emperor Qin (then aged 13) ascended the throne, and the project eventually involved 700,000 workers. Geographer Li Daoyuan, writing six centuries after the first emperor’s death, recorded in Shui Jing Zhu that Mount Li was a favoured location due to its auspicious geology, “famed for its jade mines, its northern side was rich in gold, and its southern side rich in beautiful jade; the first emperor, covetous of its fine reputation, therefore chose to be buried there”. Sima Qian wrote that the first emperor was buried with palaces, towers, officials, valuable artifacts and wondrous objects. According to this account, 100 flowing rivers were simulated using mercury, and above them the ceiling was decorated with heavenly bodies below which were the features of the land. Some translations of this passage refer to “models” or “imitations”; however, those words were not used in the original text, which makes no mention of the terracotta army. High levels of mercury were found in the soil of the tomb mound, giving credence to Sima Qian’s account. Later historical accounts suggested that the complex and tomb itself had been looted by Xiang Yu, a contender for the throne after the death of the first emperor. However, there are indications that the tomb itself may not have been plundered.
Source From: https://en.wikipedia.org/wiki/Terracotta_Army#History