The "Liquid Land" deep inside the underground palace: How the pomegranate tree revealed the mystery of the mercury mine in the Qin Shi Huang Mausoleum

Over two thousand years ago, Emperor Qin Shi Huang used mercury to simulate rivers and mountains, intending to preserve the empire’s territory forever within the underground palace. Today, modern technology gradually uncovers this sealed history through an unlikely observation object—the small pomegranate trees growing on the fill mound.

The Trees’ “Accusation”: Silent Evidence of Mercury Pollution

Walking into the Qin Shi Huang Mausoleum area, one detail immediately catches the eye: the pomegranate trees atop the fill mound are unusually dwarfed, with an average height of less than 1.5 meters, twisted branches, and sparse leaves. This starkly contrasts with their counterparts outside the mausoleum, which are three to four meters tall and lush.

Geological sampling in 2002 revealed the answer. Detectives found that the mercury content in the soil around the roots of these pomegranate trees reached as high as 1440 ppb, 80 times higher than normal soil. The mercury adsorption in the leaves exceeded food safety standards by 20 times. The dwarfing of these trees is not a natural phenomenon but the result of long-term underground mercury vapor “poisoning.”

Mercury vapor is seven times heavier than air, depositing around the roots and preventing plants from absorbing minerals like iron and magnesium, ultimately hindering chlorophyll synthesis and stunting growth. Archaeologists conducted comparative experiments: poplars planted in mercury-contaminated areas showed that after three years, the ring width near the center was only one-third of that at the edges. Due to their hardy roots and strong resistance, pomegranates became one of the few tree species capable of surviving in such extreme environments—and also serve as natural “mercury pollution indicators.”

How Geological Data Maps the Ancient Empire

In 1981, a geological team conducted the first mercury content measurement within a 12,000-square-meter area at the center of the fill mound. The results shocked everyone: mercury concentration showed a ring-shaped distribution, with the highest levels reaching 25 times that of surrounding farmland.

To eliminate interference from the soil’s natural mercury levels, the team specifically collected soil from the original source of the fill—fish pond soil—for comparison. The mercury levels in normal soil were completely within standard ranges. This confirmed that the abnormal mercury concentrations indeed originated deep within the underground palace.

Even more astonishingly, the distribution pattern of these mercury anomalies perfectly matches the records in the Records of the Grand Historian. According to the measurements:

• Highest concentration in the northeast, corresponding precisely to the Bohai and Yellow Seas within the Qin Empire’s territory
• Second highest in the south, aligning with the Yangtze River basin
• Almost no anomalies in the northwest, which is the origin of the Qin state in Longxi—an arid region historically with little water

Sima Qian’s description of “using mercury for all rivers and streams” is not just poetic exaggeration but an accurate depiction of the actual layout of the underground palace.

From Mining to Smelting: The Industry Chain Two Thousand Years Ago

Experts, based on the excavation scope of the underground palace (170 meters east-west, 145 meters north-south) and the depth of mercury anomalies, estimate that if the mercury layer averages 10 centimeters thick, the total reserves could exceed 100 tons. What does this figure truly signify?

It must be understood within the context of mining during the Qin and Han dynasties. At that time, large-scale extraction of cinnabar in the Bayu region and mercury in Xunyang, Shaanxi, had already been established. Over 3,000 ancient mines have been discovered in the Xunyang area, and Qin-era pottery jars excavated there confirm it was a major mercury smelting site.

Based on Qin-era distillation technology, 1 ton of cinnabar could produce approximately 0.86 tons of mercury. To produce 100 tons of mercury, at least 116 tons of cinnabar raw material would be needed. This amount corresponds to several years of production in the Bayu mines, supplemented by Xunyang, to meet the enormous demand for the underground palace construction.

Structural Verification: How Mercury Rises to the Surface

Geophysical survey data further deepens this mystery. At 34 meters beneath the fill mound, the stone palace walls are well preserved; the tomb chamber’s ceiling is 72 meters below the surface. Analysis suggests the mercury layer is most likely located at the bottom of the tomb chamber.

Over two thousand years, mercury vapor has slowly risen along the cracks in the rammed earth, forming a “mercury gas belt” in the middle of the fill mound, precisely affecting the growth of surface vegetation. In 2025, LiDAR scans revealed 12 radial fractures, 2-5 centimeters wide. These natural channels act like “highways,” facilitating the diffusion of mercury vapor.

The distribution of mercury anomalies at depth aligns perfectly with the internal structure of the underground palace, further confirming that mercury is stored deep underground and continues to volatilize upward.

Modern Warnings: Management Considerations Behind the Trees

Today, staff at the mausoleum regularly prune these slow-growing pomegranate trees to prevent fallen fruit from polluting the environment. Visitors are advised to wash their hands immediately after touching the tree trunks—since the mercury adsorbed on the bark can reach 0.5 ppm. While short-term contact is harmless, long-term accumulation warrants caution.

From ancient relics to modern environmental protection, these seemingly ordinary pomegranate trees carry a dual identity: they are physical witnesses to the ambition of Emperor Qin Shi Huang’s empire, and natural warnings that modern humans must respect.

Conclusion: An Ever-Moving Silver River

These twisted-branch pomegranate trees, with their two-thousand-year growth record, testify to a sealed history. They tell of Qin Shi Huang mobilizing the entire nation’s resources to cross mountains and rivers to mine mercury, forever sealing the empire’s “liquid mountains and rivers” underground. As modern technology gradually reveals these hidden pasts, we truly understand that history exists not only in words but is also engraved in the land and life itself.