Petrographical and geochemical criteria for a chronology of Roman mortars between the 1st century BC and the 2nd century AD: the Curia of Pompey the Great

Thirteen samples of mortar collected from different masonry structures of the Curia of Pompey the Great and from three mixtilinear basins located within the Sacred Area of Largo Argentina of Rome were studied. Despite the use of the same volcanic deposit, known as ‘Pozzolane Rosse’, to produce the fine aggregate in all these mortars, it was possible to highlight some distinctive features through the combination of geochemical analyses on selected trace elements and petrographic analysis under an optical microscope, allowing the three groups of mortars to be distinguished. These types of mortars reflect a perfect coincidence between the diversity of the volcanic materials used and the different construction phases identified and documented by the analysis of the stratigraphic units: a first construction phase of Pompeian age, a second phase of Augustan age and a final phase in the medieval period. Furthermore, it was possible to ascertain two phases of construction of the basins, the second coeval with the interventions of the Augustan period. Finally, this study increases knowledge about the methods of exploitation and selection of volcanic materials used to produce mortars in the Roman period, identifying additional elements useful to establish their origin and chronology of use.