Chemical compositional data of the corrosion products on Late Roman military crossbow brooches. A comparative study

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This paper presents an original dataset of 155 non-destructive surface pXRF analyses on 52 Late Roman crossbow brooches from the military cemetery at Krefeld-Gellep (Germany). These were gathered with the aim to characterise Late Roman military metallurgy, in particular where it concerns the role of state-controlled production, potential evidence for standardisation of manufacturing and the extent of recycling that took place of copper alloys at the time. It was found that although brass is often touted as an alloy particularly closely associated with the Roman army, it played a very limited role in the production of the crossbow brooch from Krefeld-Gellep, which instead were characterised by heavily leaded gunmetals and bronzes. Despite the prevalence of these complex alloys and the likelihood that these were arrived at through (prolonged) recycling and mixing, this paper concludes that Late Roman smiths were still able to make informed decisions about which materials to use. This is demonstrated by the preference of high-lead copper alloys for military dress accessories, while contemporary civilian dress accessories appear to have been predominantly made of a lower leaded, high-tin copper alloy.