One of the most interesting aspects of the tomb of China’s first emperor, Qin Shi Huang Di, is the extent to which the burial chamber may survive undisturbed. In spite of the long-held assumption that Han Dynasty accounts of looting meant that the tomb had been violated, there is increasing evidence that the destruction was confined to marginal areas of the huge funerary complex.

Recent scientific work, described by the Chinese archaeologist Duan Qingbo in the catalogue for the British Museum’s exhibition The First Emperor: China’s Terracotta Army, includes measurement of the amount of mercury in the soil on the central burial mound, a hill of rammed earth visible for miles around. Originally some 515m by 485m (1,675ft by 1,575ft) in size, the mound is now just more than two thirds of that in area as the result of erosion and sedimentation around the base.

A survey in the 1980s showed unusually high levels or mercury, up to 1,500 parts per billion (ppb) on top of the mound, against an average background beyond the mound of 30ppb.

The new work “affirmed that there is an unusally high level of mercury around the centre of the mound, and that high mercury levels are restricted to the tomb area”, Duan, of the Shaanxi Institute of Archaeology, says.

The Han historian Sima Qian recorded that the tomb chamber was an “underground palace” which held a map of the Qin territories on which the rivers were picked out in liquid mercury; because the metal vapourises, it was thought that if this were true, the resultant gas might have contaminated the soil above during the 2,200 years since the First Emperor was buried.

“Moreover, the distribution of mercury level corresponds to the location of waterways in the Qin empire — there is no unusual amount of mercury in the northwest corner of the tomb, while the level is highest in the northeast and second highest in the south.”

That the mercury seems to be still concentrated in a regular pattern “suggests that the underground palace has not been subjected to large-scale disturbance and burning.

“The plan of the underground palace can be deduced from the signals of the magnetic anomaly, due to the difference in density between compacted earth and natural earth. The gravity-inversion method shows that the cross-section is like an inverted truncated pyramid,” Duan says.

The palace itself was constructed at the bottom of a deep, stepped pit, some 170m long and enclosed by a wall of rammed earth which, Duan calculates, was 145m from east to west and 125m north-south. It stood 30m high and was 15m thick at the top.

The tomb chamber within was built on just as grand a scale, some 80m long and 50m wide, with a height of about 15m. It was reached by a series of ramps, the main entry being on the east side; on the west a passage led to a pit filled with half-scale bronze chariots and horses.

Sima Qian noted that the tomb was dug below the water table, and a complex of diversionary dams and drains was built to steer groundwater away from the burial. The tomb was also sealed, and the use of surface nuclear magnetic resonance shows that water has been kept out of the chamber since it was constructed.

Two conclusions from the scientific work are that the chamber has not collapsed — a void is still present, suggesting that the burial goods are likely to be still in place — nor has it been looted.

“Tomb robbing on a small scale has been discovered around the perimeter of the mound and the outer surface of the underground palace,” Duan says. “Scattered ashes, fired earth, broken bricks and tile fragments were found, suggesting that the above-ground buildings in the tomb complex were burned at the end of the Qin Dynasty.”

The Pottery Army was also looted and burnt, but Qin Shi Huang Di himself apparently still lies where he was entombed at the birth of the Chinese empire.

“Since the mound is still well preserved, it cannot be proved that Xiang Yu \ robbed the imperial mausoleum after the death of the first emperor,” Duan concludes.

For further discussion see The First Emperor, edited by Jane Portal. The exhibition opens at the British Museum today