Comparative study of pozzolanic mortars of the imperial roman period: examples from italy, Portugal, and Greece

Abstract

This study offers a comparative archaeometric investigation of pozzolanic mortars from three Imperial Roman contexts — a taberna in Ostia Antica (Italy), Villa Santa Suzana (Portugal) and the Villa of Herodes Atticus close to Doliana (Greece) — aiming to link technological choices to local resources and function inside a structure. A total of nine samples were characterized through complementary methods: macroscopic and stereomicroscopic description, granulometry, X-ray diffraction (XRD) for mineralogy, SEM-EDS for microstructure and elemental composition, Atomic Absorption Spectroscopy and Loss on Ignition for bulk chemistry, ion chromatography for soluble salts, and multivariate statistics (PCA, PERMANOVA, hierarchical clustering, correlation analysis) to synthesise trends. The results demonstrate a consistent technological intention to produce pozzolanic mortars across all sites, though achieved through different material strategies. Analytical data show that Ostian mortars employ natural volcanic pozzolana, whereas those from Villa Santa Suzana and the Villa of Herodes Atticus achieve hydraulic properties through artificial pozzolana, crushed bricks and tiles. Variations in granulometry, porosity, and binder-to-aggregate ratios align with functional roles inside the structures, distinguishing plasters, structural mortars, and pavements. Multivariate statistics reinforce these patterns, revealing standardized practices within each site and marked compositional contrasts between them. These findings illustrate how Roman builders balanced empire-wide technological knowledge with pragmatic adaptations to local resources. These results underscore the interplay between shared Roman technological knowledge and regionally adapted practices. The study highlights the value of multi-method archaeometric approaches for understanding ancient construction technologies and provides a basis for future provenance research and conservation strategies.