A Study on the Structural Transformation and Technological Development of Iron Smelting Furnaces in the Chungju Region

This study investigates iron-smelting sites in the Chungju region from the Proto–Three Kingdoms to the Goryeo period, with the aim of quantitatively analyzing the structure and dimensions of furnaces and clarifying the continuity and transformation of iron-smelting technology on the Korean Peninsula. Chungju, located within the Okcheon metamorphic belt, possesses abundant iron ore deposits of moderate grade, extensive forest resources that ensured a stable charcoal supply, and the Namhan River waterway that enabled effi cient transportation. These favorable conditions fostered the concentration of iron-smelting sites throughout the Proto–Three Kingdoms, Three Kingdoms, and Goryeo periods, making Chungju a persistent inland center of iron production. Structural and metric analyses revealed significant technological evolution. Ancient furnaces are characterized by circular ground plans, elaborate subterranean structures composed of layered clay and wooden posts, and the direct insertion of large-diameter tuyeres into the furnace body. In contrast, Goryeo-period furnaces adopted elliptical ground plans with simplifi ed slag-outlet divisions, resulting in improved operational effi ciency. The Wano-ri II site notably exhibited an integrated arrangement of the underground air-supply facility, furnace body, and tuyere system. The tuyere was inserted from the rear at an angle of approximately 17°, maintaining a distance of about 10 cm from the furnace bottom — a design that simultaneously enhanced air-blowing effi ciency and the durability of the tuyere itself. Based on quantitative measurements, the average furnace area in the Goryeo period was approximately 1.37 m², about 49% smaller than the ancient average of 2.68 m², while the average depth increased. This indicates a clear trend toward miniaturization and vertical deepening rather than large-scale enlargement. Such transformation reflects technological optimization aimed at maximizing air-blowing responsiveness, thermal retention, and operational effi ciency, rather than a decline in production capacity. Furthermore, operational patterns shifted from parallel operation of multiple furnaces (up to fi fteen at the Chilgeum-dong site) to small-scale, high-effi ciency systems with only one to three furnaces per site during the Goryeo period. Observations of vitrifi ed and heat-hardened inner walls at sites such as Wano-ri and Bon-ri further suggest a progressive development toward higher-temperature, blast-furnace-like operation. In conclusion, the Chungju region functioned not merely as a source of raw materials but as a dynamic technological hub where innovations in smelting were accumulated, refi ned, and transmitted. The continuous improvement of furnace structures, from the sophisticated subterranean designs of ancient furnaces to the integrated tuyere systems of the Goryeo period, demonstrates the internal evolution of Korean iron-smelting technology rooted in regional traditions rather than exogenous infl uences. The Chungju iron-smelting sites thus provide critical evidence for understanding the temporal continuity and spatial centrality of iron production in Korean technological history. The quantitative dataset and structural analysis presented in this study off er a solid foundation for future experimental reconstructions, comparative regional research, and material analyses, contributing to a more comprehensive restoration of the technological genealogy of Korean iron production.