Production technology of historical mortars: The Tomb Chamber of the Holy Aedicule in Jerusalem

The present study examines historical mortars collected from the Tomb Chamber of the Holy Aedicule in Jerusalem, with the aim of elucidating their production technology in relation to the monument’s historical phases. The samples were obtained within the framework of the integrated rehabilitation project conducted by the interdisciplinary team of the National Technical University of Athens. Petrographic and mineralogical data derived from optical microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and X-ray diffraction were interpreted alongside information on regional geological sources. Physicochemical analyses, including sieve analysis, stereomicroscopy, Differential Thermal and Thermogravimetric Analyses, μ-Raman and ATR-FTIR spectroscopy, were also performed. The results indicate that gypsum served as both binder and aggregate in most mortars across the various construction phases, reflecting a long-standing tradition of its use over the centuries. High-temperature phases such as wollastonite and a srebrodolskite-like mineral confirm the exploitation of gypsum derived from the pyrometamorphic Hatrurim Formation, while bioclastic limestone aggregates correspond to typical Judea Group lithologies. Three groups of mortars were distinguished, corresponding to production technologies associated with successive historical phases: (1) Late Roman–early Byzantine mortars (335–345 AD), comprising a gypsum-based binder with minor calcite and mixed aggregates, containing charcoal, carbonized plant fragments, and a natural resin particle indicative of a sophisticated technological approach; (2) 11 th –16 th century mortars, characterized by a gypsum-based binder containing calcite and Si–Al/Si–Al–Mg phases, attributable either to natural impurities in the gypsum raw material or to the deliberate addition of pozzolanic material, with or without lime, intended to enhance mortars’ mechanical strength and durability and (3) 19 th -century Komnenos restoration mortars, distinguished by a carbonate-rich matrix and ceramic-rich aggregates. • Three distinct mortar groups correspond to distinct historical eras • Gypsum was used as binder and aggregate over most historical periods • Ettringite is identified as a decay product in the 19 th century mortar • Constantinian mortars contain organic additives showing advanced material knowledge • Use of regional geological resources (Hatrurim Formation, Judea Group) is deduced