Mortars and plasters at Herod's Caesarea Maritima: integration of imported and local construction technologies

Abstract Building materials from different architectural elements at Herodian Caesarea Maritima (22–4 BCE ) provide evidence for a variety of compositions tailored to specific construction functions, demonstrating the extent of Roman technological influence on Herod's architectural program. Samples representing four functional categories (bedding mortar, pointing mortar, plaster, and mortar rubble core) were collected from walls, foundations and roofing systems in the Augusteum vaults, Promontory Palace, southern fortification, and the Herodian phase of the theatre. These samples were characterized petrographically, mineralogically and chemically, revealing three distinct binders: lime-based mixtures, lime–gypsum composites, and pure gypsum. Binders mixed with volcanic ashes were associated with opus caementicium, while additives such as organic ash were associated with Phoenician-Punic technology. Lime–gypsum binders, as well as organic ash additives, were found in bedding mortars, plaster and pointing mortar applications. Volcanic ash was found in mortared rubble cores. All materials show grading systematically calibrated to functional requirements, from fine pointing mortars (≤ 3 mm) to coarse structural materials (≤ 15 mm). These results show that builders in Herod’s construction at Caesarea employed flexible, non-standardized construction strategies to architectural elements, adapting local and imported building techniques to produce structural functions. This positions Caesarea Maritima as a laboratory for technological experimentation that fundamentally transformed regional construction practice.