A geo-referenced radiocarbon database for Early Iron Age sites in sub-Saharan Africa: initial analysis

Abstract

We report on the compilation of a new geo-referenced database of Early Iron Age dates for the regions associated with the expansion of Bantu-language speaking peoples in sub-Saharan Africa. We explore the database as a source of coarse-grained evidence of ecological constraints on site location, and as a source of evidence for large-scale spatial trends in dates for first arrival and subsequent in-filling. It is evident even at this very coarse spatial scale that Early Iron Age sites are not typically found in areas with very low or very high annual rainfall. Four hundred millimetres of annual rainfall seems to be an effective minimum for Early Iron Age sites, although the database contains a few outliers located in areas where present-day rainfall is slightly below that threshold level. It is also evident that Early Iron Age sites are preferentially found in locations that provide suitable habitat for growing seed crops of tropical origin, such as sorghum. It is not clear that there is any temporal delay differentiating the arrival of the Early Iron Age in the 10°S-20°S band from its arrival in latitudes farther to the south, with visibility increasing markedly in both latitudinal bands at about AD 200.