In February 1897, some 1,200 British soldiers raided the Kingdom of Benin in what is now southwestern Nigeria, razing the Edo people’s capital, killing civilians and exiling the oba (or king). The invaders then built a golf course on the grounds of the former royal court.

During the attack, the British looted thousands of cultural treasures, among them a group of sculptures and plaques known as the Benin Bronzes. Praised for their artistry by even the most ardent of European colonizers, most of the bronzes (in actuality made mainly of brass) are housed in museums and institutions across the globe.

Earliest known photograph of the oba's compound in Benin City, May 1891
Earliest known photograph of the oba's compound in Benin City, May 1891 Public domain via Wikimedia Commons

Amid a powerful push to return the stolen sculptures to their home country, researchers are offering new insights on the bronzes’ origins. Writing in the journal PLOS One, a team led by Tobias Skowronek details the first scientific link between the metal used to craft the artworks and manilla bracelets, a form of currency used in the trans-Atlantic slave trade.

“Finally, we can prove that the brass used for the Benin masterpieces, long thought to come from Britain or Flanders, was mined in the Rhine region between the borders of Germany and Belgium,” says Skowronek, an archaeologist at the Georg Agricola University of Applied Sciences in Germany, in a statement. “The Rhineland manillas were then shipped more than [3,900 miles] to Benin.”

Brought back to Europe after the 1897 raid, the Benin Bronzes—featuring images of humans, animals, religious subjects and more—were quickly recognized as stunning artworks. In 1919, for instance, Felix von Luschan, a curator at the Ethnological Museum in Berlin, wrote that the sculptures “stand among the highest heights of European casting. Benvenuto Cellini could not have made a better cast himself, and no one has before or since, even to the present day.”

The bronzes’ craftsmanship complicated European notions of Western superiority over African cultures and civilizations. Much about their creation mystified European scholars, from the raw materials used to make the sculptures to the techniques used to cast them.

Detail of a manilla bracelet from a Flemish trader that sank in 1524
Detail of a manilla bracelet from a Flemish trader that sank in 1524 © Ana Maria Benito-Dominguez

Almost 130 years after Britain’s attack, researchers in the German city of Bochum are drawing on advanced technology to unravel the bronzes’ secrets. Skowronek, who works out of the German Mining Museum’s laboratory, has spent several years searching for manillas sunk on ships involved in the trans-Atlantic slave trade between the 16th and early 19th centuries. Named after manus, the Latin word for hand, or manilla, a Spanish word for bracelet, manillas were horseshoe-shaped objects exchanged for gold, ivory and enslaved people. They had little value in European society and were designed chiefly for bartering in West Africa.

“There’s a deep irony that wrecks are tragedies-turned-perfect environments for studying ancient metals and commerce,” says Skowronek. “Underwater, everything from lead to gold and silver ended up frozen in time.”

Skowronek and his colleagues focused the new analysis on 67 manillas from five shipwrecks off the coasts of Spain, Ghana, the United States and England. (As a co-author of the report, I helped Skowronek’s team access the shipwrecked manillas.) The largest study of manillas to date, the project aimed to use lead isotope analysis to pinpoint where the bracelets were produced.

“Lead isotope analysis is a powerful tool, because everything non-ferrous”—alloys or metals lacking in iron—“has lead in it,” Skowronek says. “And lead isotope signatures don’t change. If you smelt a metal, or even if it’s heavily corroded after being wrecked underwater for centuries, its composition never changes. Whether the isotope is 30 percent or just 0.1 percent lead, you can trace it and where it came from.”

A 16th-century Benin Bronze depicting a Portuguese soldier flanked by manilla bracelets
A 16th-century Benin Bronze depicting a Portuguese soldier flanked by manilla bracelets Sailko via Wikimedia Commons under CC BY-SA 3.0
A Benin Bronze plaque of an Edo dignitary in ceremonial dress and an attendant
A Benin Bronze plaque of an Edo dignitary in ceremonial dress and an attendant Bullenwächter via Wikimedia Commons under CC BY-SA 4.0

After drilling tiny amounts of powder from the manillas, Skowronek dissolved the samples in acid and “fed” them to Neptune, a car-sized machine named after the Roman god of the sea. Neptune spent the next 15 hours analyzing the metal’s lead isotopes with inductively coupled plasma mass spectrometry, a technique that measures trace levels of elements like lead and zinc.

The German Mining Museum is home to a global database of 12,000 lead isotope ratios—the largest of its kind in the world. Comparing Neptune’s findings with this library, Skowronek was surprised to discover that the three oldest shipwrecks’ manillas had similar lead isotope samples and levels of calamine, a zinc ore key to making brass. The metal used to make the manillas in the two later wrecks came from England and Wales, and was not used in the Benin Bronzes.

The earliest wreck examined was a Flemish trade ship likely chartered by Portuguese merchants from Lisbon. The vessel was lost off Getaria in northern Spain around 1524, with some 313 manillas on board. Next in the timeline was a 17th-century ship that sank in the Vigo estuary off northwest Spain with a cargo of 156 manillas. A third vessel—probably the Dutch Groeningen, which exploded near the Elmina Castle trading post in what is now Ghana in 1647—held stacks of brass basins, 3,800 glass beads, cowrie shells and 636 manillas.

Some of the 313 manillas excavated from a Flemish trader lost in 1524 off the coast of Basque Country in northern Spain
Some of the 313 manillas excavated from a Flemish trader lost in 1524 off the coast of Basque Country in northern Spain © Ana Maria Benito-Dominguez

The lead isotope signatures of these ships’ manillas matched the same source: a metal-rich strip of land in western Germany’s Rhineland region. “To be honest, I would have bet on Venice, the global metal hub,” Skowronek says. “I never could have believed that mines … just one hour’s drive from my office window could have had anything to do with the slave trade.”

Nestled between the cities of Aachen, Cologne and Stolberg, the Rhineland has been a rich source of metals since Roman times. German mining was the most technically advanced on earth in the 16th century; in the 17th century, the Rhineland led the world in brass production. Brass artillery shells were still manufactured in the region during World War II.

In the next phase of the project, Skowronek compared the manillas’ lead isotopes with geochemical studies of centuries-old artworks, including the Benin Bronzes. He realized the looted Edo sculptures were made with the same German brass found in the wrecked manillas. But one mystery remained: Who shipped the manillas from Germany to the Kingdom of Benin?

“Plenty of historical sources mention mining in this area, but none touch on manillas,” Skowronek says. After taking a second look at the records, however, he “noticed commissions for what were called messing ringe, brass rings, masses of them.”

According to the documents, the brass rings used to craft the bronzes were purchased by one country: Portugal. In 1548, the Portuguese king commissioned the Fuggers, a German merchant family, to supply 432 tons of manillas (almost 1.4 million individual bracelets) over a three-year period. From the Rhineland, the brass manillas were sent to the markets of Antwerp in Belgium, then exported to Lisbon before finally being traded in West Africa.

An idealized depiction of Benin City by a 17th-century Dutch artist
An idealized depiction of Benin City by a 17th-century Dutch artist Public domain via Wikimedia Commons

Portugal’s connections to the Kingdom of Benin are well documented. Portuguese merchants first arrived in the region in the 15th century. Using manillas as currency, they quickly established a trading partnership with the Edo people. As Portuguese sea captain and explorer Duarte Pacheco Pereira wrote in the early 16th century, Edo traders came “from a hundred leagues or more up this river, bringing yams, … many slaves, cows, goats and sheep. … Our ships buy these things for copper bracelets, which are here greatly prized—more than those of brass; for eight or ten bracelets, you can obtain one slave.”

Craftspeople in Benin used the influx of brass to scale up their artistic production, melting down manillas and other imported metals to cast richly detailed sculptures and plaques. Some of the Benin Bronzes even show Portuguese soldiers and merchants surrounded by manillas.

Skowronek isn’t the first to make the connection between manillas and the Benin Bronzes. But he is the first to prove this link scientifically, shedding light on where Portugal sourced its brass.

Of all the possible sources, the Rhineland wasn’t at the top of anyone’s radar. “No textbooks link the Rhineland’s metals with the trans-Atlantic slave trade,” Skowronek says. “Germany thinks colonial slavery is none of its business. Our new science leaves no doubt that merchants and manufacturers knew exactly where their manillas were going and for what use.”

Simcha Jacobovici, co-author of Enslaved: The Sunken History of the Trans-Atlantic Slave Trade, says:

Manillas aren’t just lumps of cheap metal or a currency. They are the very symbol of the horrors of the slave trade. From the 16th to 19th centuries, Europe sent at least 20,000 tons of brass and copper to serve their nefarious deeds in West Africa. But for decades, science has lagged far behind the symbolism. Finally, that’s changing.

Today, art historians laud the Benin Bronzes as masterpieces. To Kathryn Wysocki Gunsch, deputy director of the MIT Museum and the author of The Benin Plaques: A 16th-Century Imperial Monument, “the bronzes are artworks of great virtuosity, molded masterpieces that exquisitely show even the texture of luxury cloth, jewelry and intricate bells in minute detail.”

In her book, Gunsch reconstructs the original appearances of around 850 reliefs that once covered wooden columns in the oba’s court in Benin City. Likely started between 1517 and 1550, during the reign of Oba Esigie, after a civil war and an attempted invasion by the Kingdom of Idah, the collection was finished by Esigie’s son Orhogbua between 1550 and the 1570s. This timeline places the bronzes’ creation at the height of the Edo people’s trade with Portugal, when brass manillas were readily flowing into Benin.

A Benin Bronze depicting two Portuguese merchants with manillas
A Benin Bronze depicting two Portuguese merchants with manillas Metropolitan Museum of Art under public domain
One of the Benin Bronzes returned by the Smithsonian Institution in October 2022
In October 2022, the Smithsonian Institution returned 29 Benin Bronzes (including the one pictured here) to the National Commission for Museums and Monuments in Nigeria. Franko Khoury, National Museum of African Art

“The plaques showed the ideal relationship between a king and his court at a time of political strain,” says Gunsch. “You can see religious rites, processions, battles and subjects paying taxes. Not only are the reliefs beautiful, [but] they have also always been valuable. Brass was currency in the 16th century, and the plaques made a big statement. It was as if a president wallpapered the White House with $100 bills.”

So much of the story of the Benin Bronzes is wrapped up in myth. The Edo people were not an “assembly of degenerate and feeble-minded posterity,” as European colonizers later claimed to justify their conquests. And the reasons for the “punitive expedition” that brought the sculptures to the West are more complex than the British initially claimed. While the British said they’d targeted Benin in retaliation for an Edo ambush of a trading expedition in January 1897, they had likely planned the attack far earlier, with the aim of securing the British Empire’s trade interests in palm oil and rubber.

In the Edo language, the verb sa-e-y-ama means “to remember” by casting a motif in bronze. More than 400 years after the first Benin Bronzes’ creation, science is now pushing the present to faithfully remember the past, from Germany’s long-overlooked role in the slave trade to how Europe’s cheapest metal helped produce the finest art in West Africa.

Get the latest History stories in your inbox?

Click to visit our Privacy Statement.