It’s not easy to extract iron from its ore. But the peoples of the ancient city of Great Zimbabwe—the capital of a thriving kingdom in southern Africa between 1000 to 1700 AD—were masters.

At sites near the city’s stone ruins, clusters of iron-smelting furnaces survive today as mounds of rubble. At Mashava, a village 25 miles northwest, fragments bear fingermarks of those who long ago smoothed the structures’ clay interiors.

Some of the furnaces were nearly an adult’s arm span in width, with walls thick and strong to contain the heat of more than 2,100° Fahrenheit needed to smelt iron. Unlike other furnaces that required workers to force air into them with bellows, these were designed to suck air in, then out through a chimney, no human labor required. This would have made it significantly easier to produce the iron, which was fashioned into hoes, axes, and arrowheads.

“The number and size of these furnaces, together with the use of natural-draft technology, indicate intensive and technologically sophisticated iron production,” says archaeometallurgist Ezekiel Mtetwa of Chicago’s Field Museum of Natural History, who has long studied the furnaces.

Scientists are extremely interested in the peoples who created this and other iron-powered societies across eastern and southern Africa. Research points to an adaptable and innovative group from western Africa as the masterminds. Known as Bantu speakers, these communities began gradually expanding across the continent’s southern half, starting from 6,000 to 4,000 years ago. In doing so, they introduced a fundamentally new, sedentary way of life—characterized by farming, raising livestock, pottery-making, and metalworking—to regions previously dominated by hunter-gatherer communities.

This migration transformed not only the region’s history and technology, but also its languages: Today, around 350 million Africans speak one of roughly 500 distinct Bantu tongues, from southern African Zulu to eastern African Swahili. And at least as many Africans—as well as many African Americans and Afro-Latinos—carry Bantu ancestry in their DNA.

Reconstructing this expansion has been a tough puzzle, especially given the region’s sparse written historical records and limited research funding. But a unique blend of scientists—linguists, archaeologists, and geneticists—have teamed up to unearth clues about the deep origins of the Bantu-speaking people, their path across Africa, and their relationships with other cultures. Although much debate and uncertainty remain, little by little the work is uncovering one of history’s largest and longest human migrations.

“It completely reshaped the demography in sub-Saharan Africa, and we are really interested in trying to understand it,” says population geneticist Sandra Beleza of the United Kingdom’s University of Leicester.

People on the move

The first evidence of the Bantu expansion came from observations of similarities among Bantu languages. They’re so alike, in fact, that when the Portuguese explorer Vasco da Gama sailed around the southern tip of Africa in 1497, a Portuguese crew member who had spent time in west-central Africa could reportedly communicate with locals in southeastern Africa.

Linguists working in the 19th century started referring to the language family as Bantu, the plural of muntu, meaning “human being” in many Bantu tongues. Later linguists reasoned that the languages stemmed from an ancestral people who migrated across the continent from western Africa, which harbors the greatest diversity of Bantu languages (as would be expected for where the languages originated).

Soon, archaeologists found supporting evidence: across eastern and southern Africa, pieces of pottery of similar yet diverse styles, alongside first-time traces of village life, metal-making, domesticated animals, and western African crops—all developed within the last 2,000 years. Northern sites usually dated back to earlier time periods than sites farther south. “You can clearly see a north-to-south progression,” says archaeological scientist Shadreck Chirikure of the University of Oxford.

By the 1990s, however, some scholars began to question the idea that Bantu languages and skills spread through a migration. Couldn’t these cultural habits have spread while people stayed in the same place, with hunter gatherer communities passing along new technologies, languages, and habits to each other?

Genetic techniques that could analyze people’s ancestry helped to resolve that debate. All of us share DNA with our relatives: 50 percent on average with siblings, 12.5 percent with cousins, 3.3 percent with second cousins, and so on. Though these proportions become minute the further back in time a shared common ancestor lived, statistical techniques can tease out patterns.

Sure enough, a 2009 genetic analysis of 2,432 Africans found that Bantu-speaking people from western, central, and southern Africa are much more closely related than one might expect given their geographic distance. And in 2024, a team of scientists analyzed the genomes of 1,763 Africans and found the greatest genetic diversity among Bantu speakers in western Africa. As distance from the region increased, diversity declined. “This is a typical signature of a population expanding from one place to another,” explains coauthor Carina Schlebusch, a geneticist at Uppsala University in Sweden.

Roughly 350 million people across sub-Saharan Africa speak one of roughly 500 Bantu languages—from Swahili in eastern Africa to Xhosa spoken in southern Africa.

Mysterious roots

But while linguistic and genetic data point to western Africa—particularly the Grassfields region of Cameroon—as the Bantu homeland, conclusive archaeological proof is thin. At the best-studied archaeological site in the Grassfields, a rock shelter called Shum Laka, pottery fragments appear dating from 7,000 to 6,000 years ago and become abundant by 5,000 to 4,000 years ago. Bowls and jars at first decorated simply with incisions and stamps and later bearing the marks of carved or braided tools rolled over wet clay are a possible, yet inconclusive, trace of Bantu ancestors.

South of Cameroon, archaeologists have searched for artifacts in one of the Bantu-speaking people’s first destinations: the Congo rainforest. A handful of times between 2010 and 2023, archaeologist Alexandre Livingstone Smith of Belgium’s Royal Museum for Central Africa traveled via boat along the Congo River as part of a team led by linguist Birgit Ricquier. In a number of villages, Smith found pottery shards of a style consistent with that found farther west, dating back to 2,300 to 2,000 years ago. “That would be the potential first Bantu settlers of the forest,” Smith says.

Many experts interpret the trails of pottery as evidence that ceramics traditions were brought by Bantu-speaking people all the way from their original home. What’s unclear, however, is when and how Bantu-speaking peoples acquired their farming and metalworking skills—and, in particular, whether they invented iron smelting themselves or learned it from neighboring, iron-extracting cultures.

Scientists have been able to deduce the path that Bantu speakers took to eastern and southern Africa. Some scholars have argued that the path split into two before entering the Congo rainforest, with one group heading east while another went south through the forest. But evidence is now mounting that these groups crossed the rainforest together, and only upon reaching its southern fringes roughly 2,500 to 3,500 years ago did they split into east-moving and southward-moving groups.

Some of this evidence comes from linguistic studies. Not unlike the evolution of species, languages diverge and transform over time, creating “trees” that linguists can reconstruct from similarities in grammar and vocabulary. In 2015, a group of researchers did this computationally using data from about 400 Bantu languages. They observed a much larger diversity—and deeper splits—among the Bantu languages spoken in the Congo rainforest, suggesting that Bantu-speaking ancestors spent a long time there, allowing their languages to diversify. Languages spoken farther east and farther south appeared to stem from a less diverse subset of this larger group, explains coauthor Koen Bostoen, a linguist at Belgium’s Ghent University.

Later linguistic studies, as well as genetic analyses, have reached similar conclusions. In 2023, Beleza and her colleagues compared the genomes of Bantu speakers from Angola—south of the Congo rainforest—with those from the eastern African country of Mozambique and ones from Cameroon, the Bantu homeland.

Remarkably, the eastern African samples were more genetically similar to those from Angola, hundreds of miles to the south of Cameroon and south of the rainforest, than to any of the samples from Cameroon. That points to a recent common ancestor in the Angola region—suggesting that the Bantu split into eastern and southern streams only once they reached the rainforest’s southern edge, Beleza explains.

By the time the Bantu people commenced their movement east and south, they had already come into their own as a farming, iron-making, livestock-herding, and pottery-making people, Chirikure says: Many ancient Bantu settlements across eastern and southern Africa contain evidence of this Bantu “package.”

Mixing and mingling

Key to the Bantu’s success in southern and eastern Africa, experts suspect, was their sedentary lifestyle. This—and their iron tools—would have allowed them to produce more food and grow in number, propelling them to occupy new territories. Their lifestyle affected the landscape as forests turned into farmland, and it also affected the hunter-gatherer communities who were already living there. Some groups were likely crowded out and disappeared, experts suspect, while others were probably pushed to marginal regions, including Indigenous groups such as rainforest hunter-gatherers and Khoisan peoples, who continue to live in central and southern Africa, respectively, to this day.

Still, scientists are learning that Bantu peoples had deep relationships with these two groups. In the 2024 genetic analysis, Schlebusch and her colleagues found that some Bantu-speaking groups in central Africa share about an eighth of their DNA with rainforest hunter-gatherers, and some southern African Bantu speakers share a similar amount with Khoisan groups. Clearly, their ancestors once intermixed.

Curiously, in the case of the Khoisan, this mixing tended to arise from pairings of Bantu-speaking men with Khoisan women. One 2021 study of southern African Bantu speakers found that the DNA inside their mitochondria—which people inherit only from their mothers—had greater-than-expected proportions of Khoisan DNA. But the Y chromosomes, which come from fathers, had much higher proportions of DNA with Bantu ancestry. Some experts speculate that this pattern could be the result of Bantu men raiding Khoisan women or preferentially marrying Khoisan women for whom the traditional bride prices would have been cheaper. “Whenever there is a power difference… between two groups, it tends to melt down to this,” says coauthor Ananyo Choudhury, a geneticist at the University of Witwatersrand in South Africa.

This pattern also left marks on the language. The characteristic clicks of Khoisan languages also occur in southern African Bantu languages Zulu and Khosa. Bostoen suspects that the children of Khoisan-Bantu pairings were, at first, bilingual. Eventually, “they lost their mothers’ languages, but they left a substrate of the mothers’ languages in the Bantu language.”

Archaeologists are also studying the relationships between Bantu farmers and their neighbors. While there may have been conflicts over land, the groups also cooperated with and learned from one another, says Décio Muianga, an archaeologist at Eduardo Mondlane University and the research institute Kaleidoscopio in Maputo, Mozambique. He’s been excavating a rock shelter in Mozambique containing thousands of years’ worth of stone tools, wild animal bones, and wild plant remains—telltale signs of hunter-gatherers living at the site. But interestingly, Bantu-style pottery also appears. “My assumption is that the hunter-gatherers were getting these ceramics from the farmers,” Muianga says. “They were interacting, communicating, and exchanging resources.”

There is evidence, too, for cultural exchanges: European anthropologists have reported that some Bantu-speaking groups would solicit San hunter-gatherers to conduct traditional rainmaking ceremonies, for example.

Bantu social networks eventually extended well beyond Africa. By 1100 to 1600 AD, many of the complex state societies that Bantu speakers built developed trade networks across the Indian Ocean. Archaeological data shows they imported Chinese porcelain and glass beads; in return, they exported gold, ivory, and iron. In fact, a 12th century Muslim cartographer once wrote that iron from parts of southern Africa—likely referring to Great Zimbabwe’s iron-producing hinterlands, Mtetwa suspects—was deemed to be of much higher quality than that from other places like India.

Mtetwa has found evidence that iron smelters near Great Zimbabwe would add bone fragments to the furnaces, perhaps as part of a smelting-blessing ritual, but one with scientific merit: This material contains calcium, which can accelerate the separation of iron from the rest of the ore. That may be a testament to the Great Zimbabweans’ iron-smelting skills: “Some materials introduced within ritual or medicinal practices may simultaneously have had technically beneficial effects on the smelt,” says Mtetwa.

Though they’ve made great progress in reconstructing the Bantu world, scientists are aware of, and trying to address, the limitations of their research so far.

Linguistic studies, for instance, have been a popular tool to reconstruct Bantu history, but Bostoen cautions that very few Bantu languages have been documented thoroughly enough to definitively trace linguistic trees back in time. Linguists may never get a complete dataset, because some old branches of the Bantu language family may have died out.

Another limitation of computational Bantu language-family reconstructions is that they’ve usually assumed that languages have evolved in isolation after different Bantu groups separated. But there may have been extensive cross-pollination among languages as different groups met and interacted.

In fact, when linguists factored in the possibility of contact among Bantu languages in a 2026 study, they couldn’t reconstruct the diversification patterns described by previous linguists, says coauthor Igor Yanovich of the University of Vienna, who wrote about the challenges of Bantu linguistic studies in the 2025 Annual Review of Linguistics. In his view, linguists should first focus on thoroughly documenting Bantu languages before attempting to use them to understand Bantu history.

In hopes of adding new insights, Schlebusch is working to obtain DNA from ancient human remains. By revealing the identity of people who were living in particular places at particular times, this could help to elucidate when and where different Bantu communities moved into, overlapped with, or repopulated areas. “What we see more and more in genetic data is that the movement was probably complex—that it was these ‘spread over spread’ events,” Schlebusch says.

Archaeologists, for their part, hope to fill in the vast gaps in the archaeological record of sub-Saharan Africa—by both conducting new excavations and re-examining existing artifact collections for fresh insights. But all this work requires funding for research and laboratories, especially from African governments, says Chirikure; he, like many of his colleagues, has largely relied on funding from Europe, which is limited. Without more funding, “you are not generating fresh ideas, you are not formulating new hypotheses and testing them using some of the cutting-edge science,” he says.