An insight into iron-making in the Basque Country (Northern Spain): Technical traditions from the First Millennium BC to the later Middle Ages

Abstract

This paper presents results of recent research by the Archaeology Team of the Basque Country Mining Museum aiming to contribute to a better understanding of the technology of medieval bloomery iron smelting in the Basque Country region. A mainstay of this technology is found in a particular kind of smelting furnace, presumably of wide use during the later Middle Ages, but likely to have originated much earlier. A complete series of radiocarbon (14C) dates from charcoal used as fuel indicates that the bulk of the industry that survives was concentrated in the Late Middle Ages; but also that the iron resources were exploited earlier by means of similar economic and technological strategies and points to a time frame which would cover from the 5th century BC to the 14th century AD. Intensive archaeological work has revealed almost 350 ironworks framed within this chronology. Overall, these sites represent relatively small-scale smelting sites, typically located in the mountains, equipped with a single furnace, and identifiable on the surface by the presence of large slag heaps. The paper reconstructs the engineering parameters of this process through microscopic analysis of an assemblage of technical materials such as slag, furnace walls and pieces of ore recovered from archaeological interventions in six sites ranging in date from pre-Roman to late medieval. The results show that, in spite of the chronological span, there was a common technological procedure in smelting bloomery iron, using a particular type of sunk funnel-shape tap furnace, as well as a common economic strategy for organizing the production, as small-scale ironworks next to the ore deposits where smelting and bloom consolidation were carried on.