Mineralogical and physical-chemical characterisation of Roman mortars used for monumental substructures on the Hill of San Antonio, in the Roman city of Italica (prov. Baetica, Santiponce, Seville, Spain)

Abstract

The Roman city of Italica (Santiponce, Seville, Spain) is characterised by the use of opus caementicium, especially in major public works. Many of these works appear to be connected with the expansion carried out in the early 2nd century CE, a period in which this technique attained high levels of technical achievement. Traditionally, this expansion has been regarded as the personal initiative of the Emperor Hadrian, whose family roots were in the city.

The structure chosen for our case study is unique. It is located on the eastern slope of the so-called ‘Hill of San Antonio’ and has been interpreted as a substructure, or platform, for a public area above. However, the archaeological characterisation of this structure is still limited.

The mortars used in this construction have been characterised through petrographic, mineralogical, geochemical and physical analysis. Their mineralogical composition has been analysed using thin sections, XRD and SEM. Chemical composition has been analysed by XRF. Physical properties analysed include granulometry, density, porosity, porosimetry, mechanical and hydraulic properties. Following the analyses, four types of mortar were distinguished. In all cases, their composition is lime-based and includes different proportions of other materials, such as metamorphic, igneous and sedimentary rock. In general, a planned and consistent production technology can be inferred, as shown by the careful selection of raw materials, the proportion of caementa and the homogeneity of the resulting mortar.

The analyses have provided us with important information on the way the material was prepared and used depending on the structural needs of the construction. In addition, ancient mortar is in itself a valuable historical document concerning technological capabilities and choices and their degree of development at any given time, in this case, the Early Roman Empire.