MINERALOGICAL INVESTIGATION OF THE AGGREGATE OF HYDRAULIC ROMAN MORTARS: THE AQUA TRAIANA CASE STUDY

The aim of this research is to characterize the materials, in particular the aggregate, of the hydraulic mortars of the Aqua Traiana, an ancient Roman aqueduct built in 109 AD, at the behest of emperor Trajan. This aqueduct had the task of supply water to Transtiber and its water mills in Rome. It was damaged several times during barbarian invasions and restored by Pope Paul V between 1609 and 1612, and it is still functioning today, supplying some famous fountains like Fontana dell’Acqua Paola [1,2].

Samples, collected at the caput aquae of Sette Botti (Trevignano Romano, Italy), located north of lake Bracciano, were investigated using a multianalytical approach. Thin sections were realized to study the mortars through optical microscopy (OM), scanning electron microscopy (SEM-EDS) and electron microprobe analysis (EMPA). Part of each sample was finely ground for X-ray powder diffraction analysis (XRPD). Additionally, the aggregate separated by the mortar was individually studied by SEM-EDS and EMPA.

The combination of different techniques has shown to be a powerful method to characterize the aggregate [3,4]. In fact, the mortars were composed mainly of natural materials with pozzolanic behavior, which gave to the lime mortar hydraulic properties, that enable it to settle also underwater. Vitruvius, in his De Architectura, listed different source’s location for the pozzolans. Thanks to the combination of different analyses, it was possible to discover the use of local tuffs from the Sabatini Volcanic District (where the caput aquae is located) but also of red pozzolan, coming from Alban Hills district.

1. Dembskey, E.J. The Aqueducts of Ancient Rome. Ph.D. Thesis, University of South Africa, Pretoria, South Africa, 2009.
2. Cifarelli, F.M.; Marcelli, M. L’Aqua Traiana: Infrastruttura della città antica e moderna. In Traiano: Costruire L’Impero, Creare L’Europa; De Luca Editori d’Arte, Ed.; 2017; pp. 221–226.
3. Jackson, M.; Deocampo, D.; Marra, F.; Scheetz, B. Mid-Pleistocene pozzolanic volcanic ash in ancient Roman concretes. Geoarchaeology 2010, 25, 36–74.
4. Maravelaki-Kalaitzaki, P.; Galanos, A.; Doganis, I.; Kallithrakas-Kontos, N. Physico-chemical characterization of mortars as a tool in studying specific hydraulic components: Application to the study of ancient Naxos aqueduct. Appl. Phys. A 2011, 104, 335–348.