XRF analysis of ancient Numidian coins: a comparison between different kingdoms

The aim of this study is the determination of the alloy used for coins from several North African kingdoms of the third century B.C., obtaining results that deepen our knowledge about the production of currencies in Numidia. X-ray fluorescence analysis has been applied on 69 ancient coins, issued in different Numidian cities. We focus especially on two arch-rival Numidian kingdoms: the Masaesyli in western Numidia, ruled by king Syphax, and the Massylii in eastern Numidia, under the king Massinissa. Parts of the coins from this last kingdom are lead-based, while the rest of samples are copper-based alloys. To compare different kingdom production, we performed both hierarchical clusters and principal component analyses. The samples are clearly divided in three groups: the first comprehends all Massinissa coins rich in lead (up to 98%), the second comprehend bronze coins with various ratios of copper, lead and tin, and the other show a higher presence of copper with traces such as lead and tin. These results reveal incontestable homogeneity and coherence with archaeological information, following the technological and historical evolution. Moreover, the global analysis of the data confirms the presence of two kinds of alloys, copper based and lead based; the obtained analytical data allow making some considerations about the minting of bronze and lead coins during the historical period of Numidia.