Terracotta Army Preservation Mystery Solved by Scientists

Terracotta Army
View of Pit 1 of the Terracotta Army showing the hundreds of warriors once armed with bronze weapons. Xia Juxian

A long standing mystery about the preservation of China's Terracotta Army appears to have been solved. The weapons, once thought to have been coated in some advanced anti-rust technology, was actually preserved by accident due to the natural conditions in which the monument was erected.

Marcos Martinon-Torres, from the Department of Archaeology at the U.K.'s University of Cambridge, was part of a project to understand how the Terracotta Army came to be. The collaboration between researchers in the U.K. and China looked at how the ancient civilization brought together technological knowledge, artistry, labor and materials to "create something as large and sophisticated as the First Emperor's Mausoleum," he told Newsweek.

The Terracotta Army, which dates to between 210 and 209 B.C., was built for Qin Shi Huang, the founder of the Qin dynasty and first emperor of a unified China. The army consists of 8,000 soldiers, 130 chariots, 520 horses, and 150 cavalry. It was buried with the emperor, supposedly protecting him in the afterlife.

Since its discovery in the 1970s, scientists have been working to understand how the monument was built and preserved. Its bronze weapons were found to have traces of chromium on them, which researchers believed may have been purposfully applied to help prevent rust.

"We were always fascinated by the possibility that Qin artisans might have used some form of super-advanced technology in order to preserve their weapons for the afterlife," Martinon-Torres said. "The pioneering scientific work carried out by Chinese experts in the late 1970s and early 1980s was rigorous and convincing. The results were surprising of course, but then again the archaeology of the Mausoleum is full of fascinating surprises and so the possibility of an ancient chromium-based anti-rust technology seemed plausible."

A study published in Scientific Reports has now ruled this theory out. In it, Martinon-Torres and colleagues carried out analysis of the bronze weapons and concluded the presence appears to be the result of contamination from a lacquer that was used to treat the wooden parts of the weapons.

The analysis, in which the team examined almost 500 weapons found at the site, discovered chromium was only present on 37 of them—it was most commonly found on bronze that was near handles or grips, and was rarely detected on arrow heads and sword blades.

Providing another hypothesis about why the weapons were so well preserved, the researchers argue that environmental reasons may have played a part. This includes the high tin content of the bronze used, and the composition of the soil at the site.

Martinon-Torres said that the discovery that the ancient Chinese had not developed an advanced form of anti-rust technology is not a disappointment. "There are plenty of other elements of the Terracotta Army that illustrate the extraordinary skill and ingenuity of Qin artisans, and so the somewhat prosaic conclusion of this particular research strand should not be seen as a let down," he said.

In terms of what the team will be working on next, he added: "In some ways the Terracotta Army feels like an extraordinary playground for archaeologists: It is large, complex, well-preserved, meticulously excavated and great fun. It raises countless questions that demand tailor-made collaborative approaches and keep all of us amused."