The Mercury Rivers of Emperor Qin Shi Huang

by Brian Dunning
April 11, 2017

Among the most amazing ancient constructions ever described is the inner tomb of the Chinese emperor Qin Shi Huang. It is said to be a vast room in which all of China is modeled in exquisite detail on the floor; the ceiling is a great arch of the night sky with pearls and other precious stones representing the stars; and most impressively of all, 100 rivers, lakes, and oceans represented by liquid mercury, flowing constantly from perpetual mechanical pumps. Could it possibly be true that this treasure room of unimaginable splendor may actually be there, waiting for an archaeologist to poke in his head? Today that's exactly what we're going to find out.

The first emperor of a unified China was given the throne at the age of only 13. He set about right away building his tomb, which took 38 years to build, and was completed about 212 BCE. In the words of the great Chinese historian Sima Qiam in his book Records of the Grand Historian:

...He had over 700,000 men from all over the empire transported to the spot.

Why so many, and why so long? Because it's really, really big, and required both an astonishing amount of skilled craftsmanship and manual labor. The workers included slaves, criminals, and conquered enemy prisoners; and DNA analysis of their bones, found in pits on the site, show they came from diverse backgrounds all over China. The construction project actually outlasted the Emperor himself. He died at about the age of 50. Construction continued for another year or two after his death before his remains were finally placed inside and it was sealed.

If you've heard anything about the Mausoleum of Qin Shi Huang, what you've heard is probably incredible. Qin Shi Huang is the same emperor who built the Great Wall of China, so we should expect his mausoleum to be no less impressive. Its best known feature is the Terracotta Warriors, full size sculptures of some 8,000 soldiers, each unique, and each elaborately clothed, painted, and armed with real weapons. A walled city, 2.2 kilometers long, encloses another, 1.3 kilometers long. And within that is the massive earthen pyramid of the tomb itself, a pyramid 350m on a side — that's two and a half times the footprint of Egypt's Great Pyramid of Giza. It's not as tall, but it's still 20% larger by volume. Think of all the impressive things you've heard about the Great Pyramid, and then consider that the pyramid at the center of the Mausoleum of Qin Shi Huang is some 20% greater by volume. Another obvious difference is that when the Chinese pyramid was completed, it was elaborately planted with trees and shrubs. Today you can walk its slopes and mistake it for a lush, old-growth forest.

Clarification: It's worth mentioning that while one of Qin Shi Huang's best known legacies is indeed being the first to unify many small local walls into a single Great Wall, the parts of the Great Wall best known today were built long after his death. So it's more accurate say he built the original Great Wall of China. —BD

The ancient Chinese believed that by placing the entire mausoleum underground, the Emperor would be immortal; and so the entire complex was dug some seven meters underground, built well below ground level, and then covered up. By core sampling and using ground penetrating radar, we know that hundreds of buried buildings lie over an area of some 100 square kilometers. The Terracotta Warriors had wood shed roofs overhead, sealed with clay to make them watertight, then several meters of soil were compacted overhead. So it was with the tomb itself, in the deepest underbelly of that vast pyramid. It was dug deepest of all, requiring the excavation of an estimated 2.8 million cubic meters of earth, "dug down to the third layer of underground springs" as Sima Qian put it, and was lined with a vermilion stone wall to keep out groundwater. It was booby trapped with automatic arrows which fired from the walls if anyone disturbed it, and lit inside with candles burning fish oil rigged to burn in perpetuity. Its crowning glory, though, was the system of flowing liquid mercury recreating the entire intricacy of China's natural waterways. When it was completed, and the First Emperor was laid to rest, the unmarried women of the court were sealed inside for the Emperor's eternal pleasure, and all the skilled craftsmen were as well, to prevent anyone from learning of the tomb's secrets. Sima Qian described it:

Replicas of palaces, scenic towers, and the hundred officials, as well as rare utensils and wonderful objects, were brought to fill up the tomb. Craftsmen were ordered to set up crossbows and arrows, rigged so they would immediately shoot down anyone attempting to break in. Mercury was used to fashion imitations of the hundred rivers, the Yellow River and the Yangtze, and the seas, constructed in such a way that they seemed to flow. Above were representations of all the heavenly bodies, below, the features of the earth.

Could these oceans and rivers of flowing mercury have actually existed? To answer that, we have to start with the very basics. Did the Chinese actually have elemental mercury in those kind of quantities?

Surprisingly, elemental mercury was relatively easy to come by in ancient China. Cinnabar, or mercury sulfide, is a reasonably abundant natural mineral that's bright red in color. Crushed and powdered, it makes a fine pigment and was well known in Chinese lacquerware since the early days of the Shang dynasty, some 1600 BCE. When that powder is simply baked in an oven, mercury vapor is released and is easily condensed and recovered as pure liquid mercury. The temperature needed is not even all that high: 357°C (675°F), well within the range of common furnaces of the time. Xunyang county in the south of Shaanxi province, the same province where the tomb is located, has a lot of ancient cinnabar mines that could have easily provided any mercury used in the tomb.

How much? Are we talking about Olympic swimming pool volumes, such as one might expect to make a "Pirates of the Caribbean"-style river complex? Chinese geologists have studied the ancient mines, and have estimated that by the First Emperor's time, they had probably produced somewhere in the neighborhood of 100 tons of liquid mercury. That sounds like a lot, and it is; but mercury is really, really heavy — 13.6 times as heavy as water. That 100 tons comes to about seven cubic meters. That's still a lot. It would make a nice big pile if you bought 7 meters of topsoil and dumped it in your backyard. But not all of this was available for the First Emperor to make his miniature rivers and oceans; in fact, probably very little of it was. The majority of cinnabar from the Xunyang quarries probably went to pigments for art and lacquerware for the entire province over several centuries.

Stories tell that Emperor Qin Shi Huang tried to become immortal by drinking vast quantities of mercury during his lifetime, only to suffer the irony of dying young from mercury poisoning. This probably isn't true. He did indeed imbibe heavily, but it was crushed cinnabar mixed with honey and wine. In this form, bound to sulfur atoms, mercury is more or less biologically inert. It is only once it's separated and purified that mercury was (and is) a potent neurotoxin. But they didn't yet know this at the time of the First Emperor, and so he — and many other people of the day — drank it prodigiously in the belief that it might confer immortality.

We can't really know how much of those seven cubic meters of elemental mercury eventually made it to the Emperor's coffers for installation at the tomb, but it was probably some amount. The historical evidence does support that the First Emperor would indeed have had the liquid mercury available to fill his miniature rivers. Probably at nowhere near the scale that the stories have led us to imagine, but enough to fulfill the historical claim. The next question to answer is whether this storied room can ever be accessed and verified.

Archaeologists are split on whether the inner tomb is collapsed, and here's why. The most significant event in the mausoleum's history came shortly after its completion. During the reign of the First Emperor's successor, there was a revolution against the Qin dynasty which resulted in the advent of the Han dynasty. Warlord Xiang Yu broke into many of the vast chambers and set them on fire, which burned the wooden beams and brought down the ceilings, crushing the Terracotta Warriors and collapsing the spaces. This is why most of the warriors found — including all of them on display at the vast covered space east of the main complex, where some 6,000 are famously displayed standing in their original rows — were shattered and had to be reconstructed. Historians recorded that Xiang Yu's fires burned for three months, smoke billowing from dozens of break-in sites the whole time. Over the centuries, farmers reclaimed the land and the vast pits of the Terracotta Warriors were all but forgotten. Suffice it to say that the chances of any undamaged remains of the tomb being discovered have diminished more and more with each passing century.

However, unlike the shallow pits of the Terracotta Warriors, the inner tomb was built primarily of rock, and was buried much deeper, perhaps as deep as 50 meters. From gravitometric studies we know the chamber measures some 50 by 80 meters wide and 15 meters high, probably at least partially collapsed. Core samples taken from the pyramid have brought some of this deep soil to light where it's been chemically analyzed, and has been found to be rich with — you guessed it — mercury. But shouldn't the mercury have remained in its riverbeds? What does this mean?

It could mean a number of things. It could mean that the chamber has collapsed and the mercury has been absorbed into the soil. It could also mean that much, perhaps even all, of the liquid mercury has volatilized away, meaning it evaporated into vapor which then penetrated the surrounding compacted soil. Mercury is a liquid at room temperature, but there are a number of factors that will influence its tendency to volatilize. Temperature, humidity, the presence of other chemical elements, even microorganisms. With over two thousand years to do so, it's a certainty that a lot of the mercury — maybe all of it — would be gone by now, even if no collapse had taken place.

Archaeologists are not likely to find out anytime soon. For now, the plan is to leave the tomb sealed and not attempt any access. It's believed that the conditions inside are too delicate. The Chinese often cite that when the first of the Terracotta Warriors were unearthed in 1974, the original paint that remained on many of them quickly deteriorated, because we didn't yet have the archaeological technology to properly protect it. We do now. We hope that in the future we'll develop a safe way to enter and explore the inner tomb, but that's not going to be anytime soon.

For now, we're going to have to leave the question of the First Emperor's incredible mercury rivers and oceans unanswered. We have strong evidence that they were in fact constructed, but to what scale we cannot say. It was probably pretty modest — even though modesty was not exactly a defining characteristic of the mausoleum of Qin Shi Huang.

By Brian Dunning
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