Unusual Use of Gypsum as a Building Stone in a Roman Bath: The Büyükteflek Bath (Central Anatolia, Türkiye)

The Büyükteflek Roman Bath, located near the Çiçekdağı district of Kırşehir in Central Anatolia, represents an important example of Roman public architecture that reflects both engineering traditions and local material utilization practices. This study investigates the architectural characteristics, geological context, and building materials of the bath complex through an integrated archaeological and geological approach. The structure, dated to the 2nd century AD, exhibits the typical spatial organization of Roman bath architecture, including the apodyterium, frigidarium, tepidarium, caldarium, and a hypocaust heating system. Architectural observations indicate that the hydraulic and thermal systems were designed according to established Roman engineering principles. Field observations reveal that the construction materials consist of a diverse assemblage of lithologies, including ultramafic, volcanic, magmatic, and sedimentary rocks, together with brick and marble elements used in different functional zones of the building. Hypocaust structures and high-temperature areas are predominantly constructed with sandstone and brick, while marble was mainly used as floor and pool lining in water-contact zones. A distinctive feature of the Büyükteflek Bath is the use of large gypsum blocks in certain wall sections. Considering the relatively low mechanical strength and high porosity of gypsum compared with commonly used Roman building stones such as marble or travertine, its use as a construction material is unusual. This choice appears to be closely related to the local evaporitic geology of the region and reflects the pragmatic use of locally available resources in Roman construction practices. Archaeological evidence also indicates that the building experienced significant functional transformations during Late Antiquity. Parts of the bath complex were reused as a small church and burial area, demonstrating the transition of the structure from a secular public facility to a religious space. Anthropological data from the associated burials further suggest that the cemetery was likely used by a socially restricted group. The Büyükteflek Roman Bath thus provides valuable insight into the relationship between Roman architectural traditions, local geological resources, and long-term building reuse processes. The results highlight the importance of considering both material properties and post-excavation environmental conditions in the conservation of archaeological structures constructed with evaporitic stones.