The unopened tomb of Qin Shi Huang

Deliberately unopened; soil surveys really do show anomalous mercury

The tomb of Qin Shi Huang, the first emperor to unify China, lies under a great earthen mound at the northern foot of Mount Li, about 35 kilometres northeast of Xi'an, in Lintong District. Work began in 246 BCE, when he came to the throne at 13, and the complex was laid out like his capital, Xianyang, with an inner and an outer city. The mound, a truncated pyramid, is given as 76 metres tall in some accounts and 51.3 metres by UNESCO. The main chamber has never been opened.

Its legend comes from the historian Sima Qian, writing in the first century BCE. He says 700,000 men were sent from across the empire; they dug through three layers of groundwater and poured in bronze for the outer coffin, built palaces and towers for a hundred officials, and filled the tomb with treasure. Craftsmen set crossbows to shoot anyone who broke in. Mercury was made to flow mechanically as the hundred rivers, the Yangtze, the Yellow River and the great sea, beneath the constellations of heaven, and candles of man-fish fat were meant to burn a long time. Childless concubines were made to follow the emperor in death, and the workers who knew the tomb's secrets were sealed inside. Some scholars, including Duan Qingbo, who led the archaeological team for more than a decade, think much of this account is fiction.

The mercury, at least, may be real. Soil surveys over the mound have found anomalously high levels, one point reaching 1,440 parts per billion and 53 others averaging around 205, though some put that down to local industrial pollution. A drainage system found in 2000 suggests the tomb was not flooded.

Around the mound lies a necropolis of more than 600 sites across 56.25 square kilometres. In March 1974 Yang Zhifa and his brothers, digging a well in a village of Lintong, struck fragments of terracotta and bronze arrowheads, and the pits they found have since yielded some 7,000 warriors and horses, each one different, facing outward to guard the dead emperor, with about a hundred wooden chariots. UNESCO listed the mausoleum in 1987. The tomb stays closed because China's heritage authorities want a protection plan first: when the terracotta figures were first exposed, their painted coats flaked away in the air, and some scholars fear the mercury would vaporise.