This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Around 700 years ago, people living on hilltop settlements on the edge of the Kalahari wore beads, bangles and clips made from metal traded across the southern half of the African continent. A new study using the chemical fingerprints of 30 metal objects has traced the source of that copper to mines scattered across four countries, some more than 950 kilometers (590 miles) away, overturning the idea that eastern Botswana was a quiet backwater on the fringe of greater political powers such as the famous Mapungubwe kingdom.
"It's amazing to think that these geological fingerprints are preserved within objects, and can tell us where their raw materials originated," said archaeologist Jay Stephens of New York University, lead author of the study published in Azania: Archaeological Research in Africa. Bosutswe, Khubu la Dintša, and Lose are a collection of Iron Age sites, the only ones with evidence of elite Lose-style pottery, each located near the headwaters of rivers that drain into the Indian Ocean, placing them at the perfect crossroads for east-west trade, the study authors wrote. Bosutswe, in particular, began as a cattle post in the seventh century, before growing into an impressive trade center boasting glass beads from Asia, cowrie shells from the coast, and a glimmering gold spiral.
These were complex societies with trade connections reaching deep into Africa and far beyond it, Stephens said. They also "constructed impressive architectural features which still exist today," he added, noting that many people living in southern Africa today are their descendants. According to the study, much is known about what these communities imported from the Swahili coast, but next to nothing about where and what they traded among themselves, including metals.
Tracing gold and iron is nearly impossible, the researchers wrote. Iron makes up roughly 7% of Earth's crust, while gold was worked from more than 1,000 small deposits across the region and was easily melted down and reused, making tracing its source akin to searching for a needle in a haystack. But copper and tin are scarcer, and each has a unique blend of lead isotopes; a geological 'fingerprint' that researchers can match with known mines across southern Africa.
Over two decades, the researchers sourced and sampled metals from all three sites and read their fingerprints. What they found was a surprising twist. Some sites in the region obtained their copper from one or two sources, like Mapungubwe which got its copper mainly from Phalaborwa, but at Bosutswe, copper came from a smattering of mines, most hundreds of kilometers away, including the Copperbelt on the Congo-Zambia border, Copper Queen in Zimbabwe, and Musina, Phalaborwa and Rooiberg in South Africa.
Curiously, of the many known pre-colonial copper mines in Botswana, only two, Selebi Phikwe and Dukwe, located just over 140 km away, show up in the artifacts. "It's a really fascinating puzzle," Stephens said. "These massive distances seem to fit an exciting trend that we are only starting to understand." A trend in which African trade networks were maintained across vast distances for centuries, one generation after another.
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