Analysis of spatial organization at two iron-smelting sites in southwestern Niger

In southwestern Niger, single-use furnaces were identified during archaeological prospecting. An exhaustive inventory of 4,504 bloomery furnaces from Saga Gorou, near Niamey, allowed us to propose a spatial analysis of catchment area of 32 km2, representing the Sahelian landscape. The smelting sites of Bilfouda and Garbel have the highest concentrations of bloomery furnaces; each was mapped accurately from low-altitude aerial photographs. Six radiocarbon dates were obtained, ranging from the fourth to the ninth century. A spatial analysis with a series of mathematical tools (Ward's method, k-means and minimum spanning tree) showed an organization of bloomery furnaces where groups were nested. Four levels from local to global were identified: battery, cluster, site and complex. Each was defined by a number of bloomery furnaces, an area, an operating time and control of production parameters. In a battery, bloomery furnaces can be arranged in a horse-shoe shape or in a more or less straight line. This organization of bloomery furnaces could be linked to the socio-cultural context and reflects good workspace management.