Credited to Rwanda. The same furnace tradition is found in Burundi and northwestern Tanzania, and the Urewe culture is named after a site in Kenya. Whether iron smelting was invented independently in Africa is debated, and the authors of the main study warn that some early dates may be centuries too old.
How it began
Archaeologists studying the Early Iron Age Urewe culture on the central plateau of Rwanda and Burundi have excavated many iron smelting sites, among them Ngoma and Nyaruhengeri in Rwanda. According to a study in the journal Historical Metallurgy, iron smelting seems to have begun in this region early in the 1st millennium BCE at the latest and flourished in the early 1st millennium CE, up to about the 7th century. Much of the fieldwork was done by Marie-Claude Van Grunderbeek from the 1980s onward.
Before it existed
The plateau offered good farming soils and easy access to iron ore and to wood for charcoal. How iron smelting reached or arose in the region is not settled. The study notes that slag-pit furnaces are unknown in the Mediterranean and the Near East, so the furnace type appears to be a purely local innovation, in Africa as in central Europe. It also says that an independent invention of smelting itself cannot easily be dismissed, though it is hard to explain chemically.
How it works
The furnace stood over a pit dug in the ground. Its wall was built up from large rolls or coils of clay, some of them decorated in a way that recalls the rims of Urewe pots. Air was driven in through clay pipes called tuyères. Inside, tiny particles of iron formed and joined together within a liquid slag that protected them from the air. The slag ran down into the pit, which was filled with grasses, and the lump of iron was taken out for forging. The slags suggest clay was part of the charge, by design or from the furnace lining.
What lasted
Slag-pit furnaces have long been recognized as characteristic of the earliest iron smelting in Africa, in both the west and the east of the continent. Iron tools changed farming and society in the Great Lakes region; a reference summary by EBSCO places the earliest ironworking between Lake Chad and present-day Rwanda by about 500 BCE. Smelting by traditional methods went on in many parts of Africa until the recent past, and former smelters have helped researchers to re-create the process.
Where it stands today
Laboratory analysis of slag, ore and furnace clay from the Rwandan and Burundian sites was published in 2007 by researchers at the British Museum with Van Grunderbeek. They found that differences in the slags came from small differences in composition and not from different processes. Survey of early smelting sites in the region has continued under the Institute of Archaeology at University College London.
