Furnace Fields: Iron Age and Roman Metalworking between York and the Humber

An archaeological investigation associated with a proposed renewable energy development at Thornton in the East Riding of Yorkshire (UK) revealed extensive evidence for middle Iron Age to early Roman industrial activity. The site demonstrates how communities adapted settlement patterns, enclosure systems and production strategies in response to changing environmental conditions. The availability of fuelwood and bog iron ore within this hydrologically sensitive setting created favourable conditions for iron production, situating Thornton within a wider zone of metalworking activity in the Vale of York. Radiocarbon dating shows that iron smelting was firmly established during the middle Iron Age, with dates clustering in the fourth to second centuries BC and extending into the late Iron Age and early Roman period. Evidence shows this to be a long-lived industrial landscape in which enclosure systems were repeatedly modified and re-cut, serving both drainage and waste-disposal functions. By the Roman period, these systems were reconfigured, with activity extending into Core Area 6, reflecting evolving land-use practices rather than abrupt abandonment. The recovery of a large quantity of archaeometallurgical residues, including a uniquely intact 155kg furnace bottom, confirms large-scale non-slag tapping slag-pit smelting employing wood pit-packing. Microstructural and elemental analyses demonstrate technological consistency across the assemblage and confirm that the residues derive predominantly from smelting rather than smithing. The large size of the furnace bottom suggests blooms were produced sequentially, rather than singly. Requiring considerable ore and charcoal, it is also suggestive of a communal effort. Similarly sized furnaces are known from the early and middle Iron Age further south in England but they are unknown from the Midlands and the North. The Thornton furnace bottom is described in detail and provides the first microstructural dataset for Iron Age smelting residues from East Yorkshire.