12th Century Swahili Bronze Coins Reveal Extensive African Trade Networks
- May 7
- 10 min read
My dad has a ‘piggy’ bank in his guest room. The modest glass jar is not meant to be savings for a rainy day. Instead, it is filled to the brim with coins from all over the world, most of them South African, some euros from Germany, others from France. There are pounds, dollars, Deutschmarks, rupees, Danish krone, and more.
Yet, something I personally never wondered about was where the metals used in these coins came from. The copper could come from Cyprus or the Congo, while the nickel may have been mined in Finland, Madagascar, or South Africa.
Today, if I wanted to, I could probably relatively easily find out the various trade networks and production points my dad’s many coins went through before arriving in our piggy bank.
This is not always the case.
In a recent study published in Azania: Archaeological Research in Africa, researchers examined the provenance of ancient bronze artifacts on the island of Ibo off Mozambique’s coast. The research proves not only the role small coastal villages played in the early development of the Indian Ocean trade routes but also may contain bronze artifacts, the copper for which was mined over 2000km away in Congo-Kinshasa, making these artifacts the most distant findings of these ores to date.
The Swahili Coast
The Swahili Coast stretches along the eastern edge of Africa, from its northernmost point in Somalia, down to Mozambique in the south. Its unique cultures and languages have long been influenced by various African, Arabian, and Indian Ocean peoples.
The original inhabitants, however, were Bantu-speaking Africans who had migrated east from the interior of Africa. From there, they spread across the coast, trading with one another as they went.
One Greek merchant’s account, written in the 1st century C.E., known as the Periplus of the Erythraean Sea, tells us that the East African city-states traded in ivory, rhino horn, tortoise shell, and palm oil.
However, in the centuries immediately following the Periplus, little is known about the history of the Swahili Coast and the trade networks they maintained.
This changed around the 8th century C.E. when Muslim traders, mainly Arabs, came to trade and even settle in the region. Various historical records were written detailing trading partners, routes, and artifacts.
By the 12th century, Persian settlers known as the Shirazi arrived, further influencing the local cultures and trade networks.
The vast majority of these 11th-15th century independent city-states were Swahili-speaking Muslim sultanates. Collectively known as ‘stone towns’ for the stone-coral blocks used to construct them.
From the 15th century onwards, the Portuguese established themselves in the Swahili Coast, after which the Swahili Coast city-states began to decline.
For much of the above history, the role of northern Mozambique has been considered marginal. This has been partially influenced by the lack of outstanding harbor stone towns.
Not only that, but the history of metallurgy in sub-Saharan Africa is also still poorly understood. Although some recent research has improved our knowledge of copper mining and metal ingots, especially in the mid-first millennium AD, there is still a lack of evidence concerning metals other than copper and iron in the region until the maritime trade with the Islamic world.
For many, the dominant belief is still that southeast African coastal traders learned about bronze metallurgy from Eurasian traders and slowly diffused this knowledge into the interior.
To make bronze, you need a small amount of tin and add that to a large amount of copper.
Despite this, the majority of copper objects discovered in archaeological excavations across the southern third of Africa are not ingots and lack distinctive shapes that would allow researchers to connect them to the Copperbelt mines in Zambia and the Democratic Republic of Congo (DRC).
Thus, to better understand the origin of these bronze artifacts, researchers have turned to chemical and lead isotope analysis, enabling them to discuss the provenance of these artifacts and the potential trade routes they may have come by.
The Quirimbas Archipelago
The Quirimbas Archipelago is made up of 50 inshore islands, some of which are uninhabited. They are located off the northern coast of Mozambique and include the islands of Ibo, which is a private island with tourist resorts for well-off foreigners.
The complex tidal regime, shallow waters, and lack of good harbors make it incredibly difficult to navigate from the islands to the mainland for most boats other than the traditional dhows.
Historically, the role and existence of the Quirimbas Archipelago have only been addressed occasionally. One of the earliest accounts was by the Muslim geographer al-Mas’ūdī in the 10th century, who wrote about the ‘land of Zanj, which likely included the Quirimbas Archipelago. According to him, the land stretched from Abyssinia (modern-day Ethiopia) to the Sofala city-state (modern province in Mozambique).
Another Arabic writer mentions a place called Sayuna, saying it was around one week’s sailing from Sofala. By the 15th century, Ibn Mājid spoke of Muslim inhabitants on the island of Wamizi, which some researchers today believe could be the modern island of Vamizi in the Quirimbas.
More concrete mentions of the archipelago appear in the form of two historical chronicles, the Pate and Kilwa chronicles. One claims that the archipelago was conquered in the 14th century, while the other mentions that in 1495, a dethroned ruler gathered his forces on Quisiya Island in the Quirimbas, hoping to reclaim his throne.
Later, Portuguese chronicles describe the Quirimbas as being active in the local textile industry, which was controlled by Muslim traders who had close links to the Kilwa Sultanate and Zanzibar.
From these accounts, it is suggested that the Quirimbas were known to, and possibly inhabited by, Muslim communities from at least the 10th century onwards.
The islands were eventually conquered in the late 16th century by the Portuguese, who wanted to take control of the gold trade between Zambezi and Kilwa. In 1634, Antonio Bocarro was the first to use the word Quirimbas to describe the archipelago. Ibo became a significant port for slaves en route to the Americas in 1820.
Ibo Island
In 2015, an archaeological research project in co-operation with the Eduardo Mondlane University of Maputo set out to investigate the involvement of the Quirimbas Archipelago in the Swahili trade network prior to the arrival of the Portuguese.
Field surveys were conducted on three islands, namely Ibo, Matemo, and Quirimba. In 2016, a small test pit was dug near the seashore and an old Portuguese fort on Ibo Island.
The top layers, which contain remains from after the arrival of the Portuguese, include remnants of imported Chinese and European ceramics, as well as some handmade local pottery.
The Portuguese fort had been built on top of an older Swahili settlement, partially destroying it. However, under the debris layers and a sterile sand dune layer, the researchers uncovered the living floor of a Swahili hut.
The semi-circular structure, dated to the 11th-12th centuries, constituted a simple hut made from wood or wattle and reeds. The hut had once had a fireplace and at least two wooden post holes. The structure was outlined by a boundary of compact trash left by the former inhabitants, including sea turtle bones, broken pottery, and beads.
The sea turtle bones likely constituted food remains. However, the other remains hinted at the island’s former role in the Swahili coast trade network.
Some of the pottery was of the local Lumbo tradition. However, others included glazed blue-green, green, and thin-walled ceramics likely from the Persian Gulf and Southern Iran.
A fragment of a soft-stone ware, possibly a lid, had likely originated in Iran and Oman. Although, around the 12th century, some soft-stone quarries were also exploited in Madagascar.
The glass beads came from India and Central Asia, while other beads were locally manufactured.
And then there were three coins, a metal chain, and some metal fragments.
Where did they come from, and how did they link Ibo to the wider Swahili Coastal trade network?
The Metal of Ibo
Let us begin with the coins. The three coins were very poorly preserved, to the point where the original inscriptions and images were impossible to decipher, save for one letter, Lam (ل). This was likely the last letter of a word or phrase, but that does not give you much context.
Imagine I gave you a coin, and all you can see is ‘r’; what will you glean from that?
One of the coins also had a hole pierced into the rim, possibly indicating it had been strung up, possibly to serve as a pendant.
To determine the origin of the metals, the researchers conducted two types of analyses. The first was elemental analysis using X-ray fluorescence (XRF).
This enabled them to determine the elemental composition of the coins. They found that the coins contained leaded bronze with very low amounts of tin and some lead. Meanwhile, the chain and metal fragments contained almost no lead and a slightly higher percentage of tin.
These compositions were compared to known Swahili ruler coins. However, the researchers found that these coins did not match any known ruler’s coin composition patterns.
You see, Swahili coins always contained at least a bit of arsenic. However, these Ibo coins had none. Additionally, they also contained a different nickel and antimony content, as well as an unusually high tin-lead ratio.
This suggested to the researchers that these Ibo coins may represent an intermediate group of coins placed between the two known chronological coin groups. This may indicate a shift in the source of copper for Swahili coins during the 11th and 12th centuries.
But where was this source?
To determine where the copper was mined for the Ibo coins, researchers employed lead isotope analyses, which helped identify the geological source of the metals.
Lead isotope analysis works by measuring the different ratios of lead isotopes (206Pb/204Pb) in a sample. These ratios serve as ‘fingerprints’ and can be compared to isotope signatures from known sources.
The researchers, therefore, took samples from two of the coins and a fragment from the chain.
Using a specialized mass spectrometer, the researchers compared the isotope signatures with sources across Africa and Eurasia.
The results showed that all the metal had originated from a single common source.
They were not from the Islamic world as their alloy composition did not match, nor were they likely recycled metal.
The researchers hypothesized that the most likely source of the copper was the Copperbelt region in Congo-Kinshasa (possibly the Shinkolobwe mine).
That is a distance of over 2000km!
This would make these the most distant findings of copper from these ores to date.
But how did copper mined in the Congo-Kinshasa make its way to Ibo?
Analyzing Ancient Trade Routes
While the poor condition of the coins and the fact that the researchers could not claim they belonged to a Swahili mintage made linking them to any particular place difficult, the researchers were able to establish a link between the Ibo coins and coins struck in Kilwa.
While the coins were slightly lighter and smaller than those of Kilwa, this may, in part, be due to their heavily eroded and poorly preserved state. One coin in particular had traces of die similar to those found on Kilwa coins.
The Quirimbas were part of the gold trade network that connected Kilwa to areas in Limpopo (South Africa) and the Zambezi, located in the Middle Limpopo Valley.
The Middle Limpopo Valley was a significant political entity that controlled long-distance trade in gold and ivory. Within it were several polities, including Mapela (ca. 1055–1450 AD), Mapungubwe (ca1220–1300 AD), and Great Zimbabwe (ca.1300–1450 AD).
There is agreement that the gold moving along the East African coast from Sofala (an outpost of the Kilwa sultinate) was likely mined from the gold belts of the Zimbabwean plateau.
This long history of trade between the southern areas of Africa and the Swahili coast helped introduce gold, tin, bronze, and brass metallurgy into these southern areas around the second millennium.
The ores required for this metallurgy, such as copper and bronze, were largely sourced locally in Botswana, Zimbabwe, and South Africa. However, some of it came from the Copperbelt.
It is possible that copper ores mined from the Copperbelt made their way through trade routes into the Middle Limpopo Valley, possibly passing through political entities such as Mapela, Mapungubwe, and Great Zimbabwe, which controlled the long-distance trade of valuable items.
From these centres, the copper may have made its way to coastal trading posts, including Ibo, which connected to Kilwa and the broader Indian Ocean trading network.
A second possible route would be one that runs through the Zambezi River, with the copper mined from the Copperbelt possibly crossing Zambia into Malawi before making its way to the coast and perhaps the islands off Mozambique.
This hypothesis may be supported by the reported ruins of several Swahili stone buildings found in the outpost of Somana, which may have served as a trade hub between the interior and the coast.
However, so far, evidence suggests that the islands of Somana and Mozambique did not emerge as trade centers connecting Kilwa until the 14th century, which is too late to have been the route used by the Ibo coins.
Additionally, the wire fragments found at Ibo resemble the bronze bangles found at stonewalled sites in Great Zimbabwe and Little Mapela, possibly indicating a trade connection between them.
Copper and bronze were of high social value in Africa. Having coins or chains made from these metals sourced from as far away as Congo-Kinshasa may have meant the Ibo coins, chain, and wire were perceived as significantly valuable personal items.
One of the coins did have a hole pierced into it, possibly indicating it was worn as an ornament, which may further suggest its high social value.
A recent study analyzing the provenance of bronze coins, wire, and a chain recovered from the island of Ibo off the coast of Mozambique offers new insights into the role Ibo island may have played in the complex trade networks of the Swahili Coast.
The study suggests that trade networks, specifically for copper, may have extended as far as Congo-Kinshasa, making the metal artifacts of Ibo some of the most distant findings of copper from these ores to date.
I wonder what journeys the coins in my dad’s piggy bank took before reaching my hands. Which mines did they originate from? Where were they minted? And how many hands have they passed through before me? How do you think the copper got to the Swahili Coast, and what other secrets may Swahili bronzes still hold?
References
Montero-Ruiz, I., Ruiz-Gálvez, M., Fernández, V., Madiquida, H., Herranz, D., & Mahumane, C. (2025). Lead isotopic provenance of some coins and other bronze items from an early Swahili site in Ibo Island (northern Mozambique). Azania: Archaeological Research in Africa, 1–26. https://doi.org/10.1080/0067270X.2025.2481762
National Geographic Society. (2022, June 2). The People of the Swahili Coast | National Geographic Society. Education.nationalgeographic.org. https://education.nationalgeographic.org/resource/people-coast/
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