The Relationship between Iron Age Hill Forts, Roman Settlements and Metallurgy on the Atlantic Fringe

Abstract

This thesis presents geochemical records of metalliferous enrichment of soils and isotope analysis of metal finds at Iron Age and Romano-British period settlements in North Ceredigion, Mid Wales, UK. The research sets out to explore whether North Ceredigion’s Iron Age sites had similar metal-production functions to other sites along the Atlantic fringe. Six sites were surveyed using portable x-ray fluorescence (pXRF), a previously unused method in the archaeology of Mid Wales. Also tested was the pXRF (Niton XLt700 pXRF) with regard to how environmentally driven matrix effects may alter its in situ analyses results. Portable x-ray fluorescence was further used to analyse testing a range of certified reference materials (CRM) and site samples to assess target elements (Pb, Cu, Zn and Fe) for comparative accuracy and precision against Atomic absorption spectroscopy (AAS) and Inductively coupled plasma mass spectrometry (ICP-MS) for both in situ and laboratory sampling. At Castell Grogwynion, one of the Iron Age sites surveyed recorded > 20 times Pb enrichment compared to back ground values of 110 ppm. Further geophysical surveys confirmed that high dipolar signals correlated to the pXRF Pb hotspots were similar to other known Iron Age and Roman period smelting sites, but the subsequent excavation only unearthed broken pottery and other waste midden development. Broken pottery remains were dated to no earlier than the medieval period suggesting a re-occupation, possibly for Pb prospection. It was established that Pb and metal rich soils within the villa footprint have similar isotope signatures to local ores found ca. 4km east, suggesting local ores were used in its construction, possibly with some evidence of in situ metal working.