652 metallurgy: Africa ing fuel since Roman times) Once gunpowder was developed in medieval China (and soon imported to the West), Chinese and European soldiers both found a ready means to exploit the new substance, by using bronze bell-casting technology to create the first cannons Perhaps the most important medieval metallurgical technology was the blast furnace This technology had been developed in China in antiquity and continued in use throughout the Middle Ages It was invented independently in Europe in the 12th century In both cases the bellows were run by complex water-powered machines The iron production of blast furnaces was measured in tons per year rather than the few pounds of iron produced by a traditional bloomery furnace Moreover, the iron produced was molten and could be easily cast The improvement and development of blast furnace technology in Europe was continuous and rapid It led to the growth of the bourgeois middle class and ultimately to the Industrial Revolution But no such transformation, either technological or social, took place in China This difference in the development of the two cultures is an important problem for the field of historical study today Africa by Kirk H Beetz By the beginning of the medieval era Africa had a long, ancient tradition of metallurgy The only cultures that may not have smelted, refined, or forged may have been hunter-gatherers and pastoralists in the Kalahari Desert and southern Africa Still, copper and iron were important parts of the lives of these peoples, who in their early recorded history would meet with outside traders who brought metal tools They would trade mostly for ostrich feathers as well as for animal skins There were places in Africa where metal was not mined but where metalworkers flourished anyway Iron and copper would be imported as ingots (a solid mass of metal), which were refined, if necessary, and then forged There were very productive copper, iron, and gold mines in western Africa, in north-central Africa, in Nubia and Ethiopia in northeastern Africa, and in southeastern Africa, and archaeologists have made significant strides in identifying their furnaces and describing how the furnaces were used There is much disagreement among archaeologists about when and how Africans began working with metal Some believe that Africans south of the Sahara learned how to work with metal from outsiders such as Carthaginians or Berbers, but archaeological evidence for this is scant Others believe metalworking began independently in sub-Saharan Africa, perhaps several times in different places Africans may have learned to work with copper first, possibly doing no more than hammering naturally occurring copper nuggets, eventually learning to identify and work with copper ore and later using their knowledge of copper to help them recognize and work with iron ore At the start of medieval times the principal metalworking sites in Africa seem to have been in two places: the land of the mysterious Nok in western Africa and in northeastern Africa, where there is ample evidence of advanced metalworking in Nubia and Axum In these areas one particular type of furnace for smelting ore predominated This furnace consisted of a large hole dug at an angle in the ground Around the surface of the hole was a bowl-shaped circle of clay This circle varied from feet to feet in height In western Africa and somewhat later in central Africa builders of the furnaces shifted from clay layered in circles to dried clay bricks and at an undetermined time in the middle of the medieval era to clay bricks that had been fired, probably by placing them directly into fires The sides of the wall would be pierced with tuyeres—openings through which air could be forced into the furnace Many furnaces for smelting and for refining had small holes in their floors apart from the main hole, and archaeologists speculate that religious or magical objects were placed in these holes to help guarantee that the smelting or refining went well These furnaces were filled with wood that was burned to make charcoal Then the charcoal was supplemented by more wood and allowed to burn until it was very hot, at which time ore was placed inside and the top perhaps covered Eventually metalworkers learned to use water to help cool the smelted metal, but this may not have occurred until late in the medieval era In general, furnaces were allowed to cool on their own, perhaps for several days When they were fully cooled, the furnaces were broken open, often with most of their walls knocked to the ground, and the smelted metal would be removed, usually mixed with ashes It is possible that this resulted in the manufacturing of steel, which combined iron with carbon from ashes Sites in the grasslands south of the Sahara and in the central forests of Africa have ditches that were dug by making a furnace, breaking it open, then making a furnace next to the old one, and so on, apparently over many generations The people responsible for these furnaces were probably nomadic pastoralists, who returned to the same locations to smelt their ore, perhaps because the spots had religious significance Among those cultures in western Africa in which traditional smelting practices survived long enough to be recorded by outside observers, pieces of clay from the wall of a previously used furnace would be incorporated into the wall of a new furnace as a way of transmitting some of the spiritual power of ancient furnaces into new ones Perhaps influenced by the