How was iron produced 2,000 years ago in Senegal? A recent study at the Didé West 1 archaeological site, in the Falémé Valley in eastern Senegal, sheds light on an ancient iron production technique.Passed down from generation to generation for nearly eight centuries, this technology appears to have been developed to meet local needs. African archaeology specialists Anne Mayor, Mélissa Morel and Ladji Dianifaba explain the significance of this discovery and what it reveals about the transmission of technical knowledge over the long term.What did you find?For over 2,000 years, metalworkers produced iron in what is now Senegal. By studying the remains they left behind, we have been able to reconstruct their technical choices, the natural resources they used, and, to some extent, aspects of their way of life. Beyond their scientific value, these studies also highlight the expertise of ancient blacksmiths, since iron production represented a major technical and social transformation, particularly for agriculture. In eastern Senegal, in the Falémé Valley, within the Boundou Community Nature Reserve, many ancient iron production sites have been identified in recent years. Archaeological surveys and excavations carried out by an international research team involving scholars from the universities of Geneva and Fribourg in Switzerland, as well as the Institut Fondamental d’Afrique Noire at Cheikh Anta Diop University in Dakar, revealed at least five distinct technical iron traditions. Read more: Why did Tutankhamun have a dagger made from a meteorite? The new study focused on one of these iron production techniques (named FAL02) identified in the region, which is represented at around 100 sites. The site of Didé West 1 (DDW1), the largest and best-preserved of these sites, stands out for two major reasons. First, it provides one of the earliest known dates for iron-smelting furnaces in Senegal. Second, it documents a long sequence of metallurgical activity spanning nearly 800 years, from 400 BCE to 400 CE. These radiocarbon dates were obtained from charcoal directly associated with the furnaces. The exceptional preservation of this site allowed us to document this technique in detail, trace its transformations over time, and better understand the choices made by the metallurgists.How were you able to prove it?The main evidence of ancient iron metallurgy comes from slag, which is the waste produced when ore is transformed into metal. During the smelting process, this slag flows like molten lava within the furnace before solidifying into rocky masses. Once the operation was completed, the slag was discarded and gradually piled up into large heaps.Our study of the Didé West 1 slag heap revealed 35 furnace bases, attesting to repeated activity over several dozen generations. Certain technical features define this tradition, including multi-perforated tuyères (clay pipes pierced with holes to allow air to circulate within the furnace), as well as the use of African palm nuts as packing material at the bottom of the furnace. This system appears to have facilitated the separation of metal from slag. Slag shaped like the seeds of the rattan palm reflects a unique cultural choice. © David Glauser, Fourni par l'auteur By combining these observations, we were able to reconstruct how this technique worked. The metalworkers used small circular furnaces equipped with a removable chimneys rather than permanent shafts. The iron ore likely consisted of laterites (a type of soil) collected from the immediate surroundings. Taken together, these elements reflect a high level of technical expertise.Who were the people behind this technology?Research on African societies during the first millennium BCE and the first millennium CE comes with several challenges. Written sources are scarce, and organic materials that could provide information about housing or diet are poorly preserved. Even iron artefacts are usually too degraded to survive.On many sites, only pottery fragments remain. It is therefore still difficult to identify precisely the populations behind the FAL02 technique. This specific technical tradition was recognised through the shapes of the furnaces, tuyères, and slag found at the sites. Iron production techniques are not merely technical processes. They reflect traditions, choices and know-how specific to each cultural group.Analysis of the slag volumes also helps estimate how much iron was produced. At Didé West 1, the data point to modest and irregular production, likely seasonal. These elements suggest that the activity was intended to meet local needs, rather than large-scale production for export.Why this mattersThe origins of iron metallurgy in west Africa are still debated. Two major hypotheses continue to be discussed. One argues that ironworking spread from the Hittite world in Anatolia (in present-day Turkey) via the Maghreb or the Nile Valley. The other suggests an independent invention in sub-Saharan Africa. To date, the available evidence does not allow a definitive conclusion. However, several ancient iron production sites dating from the first millennium BCE have been identified in sub-Saharan Africa, including in Nigeria, Niger, Togo, and Burkina Faso, and now in Senegal. These discoveries tend to strenghten the case of local development.Within this context, the dates obtained at Didé West 1, reaching at least the 4th century BCE, make it one of the earliest known ironworking techniques in Senegal. The site therefore contributes important new data to a still limited body of evidence and helps document the early development of metallurgy in the region.What happens next?This study marks an important milestone, but several questions remain unanswered. The next challenge is to better understand the other iron production techniques identified in the Falémé Valley. At least four other traditions have been recognised.Some of these techniques were in use at the same time, revealing a complex metallurgical landscape where very different traditions coexisted. This diversity raises several questions: which groups of metallurgists were behind them? How can we explain their transformations? Why do certain techniques disappear? Were some techniques more efficient than others? Read more: Traditional wrestling in Senegal - much more than a sport, it keeps culture alive The study of the FAL02 technique over nearly 800 years demonstrates that these practices evolved, with phases of continuity and transformation. By cross-referencing this data with findings from the study of ceramics and settlements, it becomes possible to better understand the societies that produced this iron and how they changed over time.These remains allow us to move beyond the purely technical question: they offer insight into settlement dynamics, the circulation of knowledge and expertise, and long-term societal transformations, even before the emergence of medieval kingdoms and the expansion of trans-Saharan trade. We hope that future research will help to answer some of these questions.Mélissa Morel receives funding from the SNF (Swiss National Fund for Scientific Research). Anne Mayor receives funding from the SNF (Swiss National Fund for Scientific research). She works for University of Geneva.Ladji Dianifaba does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.