Volcanic pozzolans are one of the most peculiar and intriguing construction materials employed in antiquity. These natural resources were extensively used by the Romans to increase the cohesive and waterproofing capabilities of ancient lime-based mortars and concretes. The most renowned one is undoubtedly the pulvis puteolana, a pyroclastic ash related to diversified Quaternary eruptions of the Phlegraean Fields and Somma-Vesuvius, that was recommended by Vitruvius and Pliny for the making of durable and waterproofed maritime opus caementicium piers and extensively traded in the ancient Mediterranean for this purpose (Brandon et al. 2014).

A recent study on mortar-based structures of the recently excavated Roman Temple of Nora (Sardinia, Italy), built in the second quarter of the 3rd c. CE, recognized the presence of volcanic pozzolans in the compounds, probably used to improve the cohesive properties of the building's concrete structures. The exact source of the raw material, not compatible with Sardinia's geology, was ascribed to the latest eruptive Phlegraean activities through advanced mineralogical and geochemical analyses (Dilaria et al. 2023). Considering Nora's location in the southern edge of the Gulf of Cagliari, the maritime transport of the material from Campania is straightforward and cost effective, but several questions arise about the actual size of the trade, which is decisive for the economic and logistic impact of the building process.

The present contribution aims to estimate the amount of the pozzolan shipped from the Gulf of Naples for the making of the Roman Temple of Nora. Material quantification was firstly achieved by parametrizing the amount of pulvis puteolana in respect to the other mortar components (i.e. sandy aggregates, lime, pores) by determining through DIA (Digital Image Analysis) the mean amount and standard deviation of material inclusions from multiple samples prepared on thin section. This "unit of measurement" was then transposed to the mortar-based portions of the building, by rescaling step-by-step the results of bidimensional DIA estimations to the structural volumetry of the temple, mapped in detail through plans, elevations and digital models for the preserved remains, but also virtually restored in its original form through 3D reconstruction of the no longer existing portions.

The theme of the origin and transport of geomaterials in the ancient world captivates archaeological studies also thanks to the substantial contribution provided in recent years by the exact sciences. This presentation aims to contribute to this topic, demonstrating how the careful and diligent use of archaeometry and metric analysis, in their broader definition as "measure of the past", helps in providing insights into ancient commercial and construction dynamics.