Catenary arches and vaults were used in Spain during two historical periods. First, the theoretical concept was used in the eighteenth century by military engineers for the construction of gunpowder magazines. Subsequently, Catalan modernist architects, such as Antoni Gaudí i Cornet (1852–1926) and Cèsar Martinell i Brunet (1888–1973) used this shape throughout their buildings. The paper assesses the geometric approximations to the catenary made by eighteenth-century military engineers and twentieth-century architects in Spain. The investigation is based on two documentary sources: the designs for gunpowder magazines found in the Colección de Mapas, Planos y Dibujos del Archivo General de Simancas, and the design by Cèsar Martinell i Brunet for the Cooperative wine cellar in Pinell de Brai (1918), preserved in the Arxiu Històric del Col·legi d’Arquitectes de Catalunya. The assessment confirms the use of the concept of the chain during these two historical periods.