Archaeologists are too scared to open up the 2,200-year-old tomb of China's first emperor Qin Shi Huang because they fear it might harbor deadly booby traps.

The mausoleum of the emperor, who ruled from 221 to 210 BCE, is located in Lintong District, Xi'an, Shaanxi. It is guarded by the iconic Terracotta Army, sculptures meant to protect him in the afterlife.

While parts of the necropolis have been explored, the tomb itself has never been opened due to fears of what might be inside.

Ancient Chinese historian Sima Qian wrote an account around 100 years after the emperor's death about possible booby traps inside the tomb.

"Craftsmen were ordered to make crossbows and arrows primed to shoot at anyone who enters the tomb. Mercury was used to simulate the hundred rivers, the Yangtze and Yellow River, and the great sea, and set to flow mechanically," the text reads, per IFL Science.

While some scientists dismiss the accounts as being fantastical, a 2020 study found that mercury concentrations around the tomb are at significantly higher levels than to be expected.

"Highly volatile mercury may be escaping through cracks, which developed in the structure over time, and our investigation supports ancient chronicle records on the tomb, which is believed never to have been opened/looted," says the paper.

The formidable and ambitious Qin Shi Huang was the first to rule a unified China, and historical reports suggest he became obsessed with drinking mercury in a misguided quest for eternal life.

He often drank wine laced with mercury, and might have died of mercury poisoning at the age of 49, per the BBC.

Fears of mercury are not the only thing stopping archaeologists from excavating the tomb, as there are also concerns that this could damage it.

The terracotta army and Qin Shi Huang's tomb complex are designated as UNESCO World Heritage Sites and remain some of the most significant archaeological discoveries in history.

This article was originally published by Business Insider.

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