High‐performing mortar‐based materials from the late imperial baths of Aquileia: An outstanding example of Roman building tradition in Northern Italy

Abstract

This study provides the first detailed insight into the composition and properties of structural mortars used in a 4th-century AD bath complex in Aquileia, the emblematic center of Roman culture in Northern Italy. Eighteen mortars, taken from different structures of the site, and three stone samples from the vaulting opus caementicium have been analyzed adopting a multianalytical approach integrating optical microscopy, X-ray powder diffraction, X-ray fluorescence, and scanning electron microscopy coupled with energy-dispersive spectroscopy. The properties of the compounds are outstanding, as revealed by the formation of hydraulic phases (i.e., Al-tobermorite and AFm) in most of the samples: the waterproofing capabilities of cocciopesto mortars are remarkable, as revealed by the formation of anthropogenic Al-tobermorite (5.5 wt%) in pool coating samples; the lightweight of the vaults was guaranteed by the use of porous caementa and pozzolanic volcanic aggregates imported from the Gulf of Naples, as demonstrated by petro-mineralogical features and chemical analysis of major and trace elements. This is the first proven case of trade in these building materials to the north of the Italian peninsula. These outcomes shed new light on the robust technical expertise of local artisans in Aquileia and indicate that the Cisalpina province was by no means a peripheral reality in the Roman Empire, as far as mortar-based materials are concerned.

Early exploitation of Neapolitan pozzolan (pulvis puteolana) in the Roman theatre of Aquileia, Northern Italy

“…Moreover, it marks the first use of this pozzolanic powder in an overground construction far from the Bay of Naples and the first analytically proven evidence in the Roman Cisalpina region. Indeed, as already briefly discussed in 55 , previous studies 95,96 on the possible presence of this product in mortar-based materials of the region were recently reconsidered. At the moment, the absence of any other evidence is not clearly attributable either to the lack of targeted research of this topic or to the actual shortage in the supply of the volcanic pozzolan from the Bay of Naples to Cisalpina in ancient times.…”

“…Besides, most of the evidence comes from Middle/Late 7,8,10,22,80,89,90 ), and Aeolian Arc Islands' volcanic products (compositional fields based on raw data from [85][86][87] ); (b) Nb/Y vs Zr/Y scatterplot of clasts' samples in relation to the fields occupied by the Roman, Tuscan and Campanian magmatic provinces (compositional fields edited from 80,89,90 ), and the Aeolian Arc Island's products (compositional fields based on raw data from [85][86][87] ); (c) Nb/Y vs Zr/Y scatterplot of clasts' samples in relation to the fields occupied by volcanic products of the Phlegraean Fields main eruptions (according to 82 ; compositional fields edited from 80,89,90 ), and Phlegraean-correlated products (pumices and scorias) of Ischia/Procida-Vivara (compositional fields based on raw data from 91,92 ); (d) Nb/Y vs Zr/Y scatterplot of clasts' samples in relation to the fields occupied by volcanic products of Somma-Vesuvius main pre-79CE eruptions (according to 93 , compositional fields edited from 80 www.nature.com/scientificreports/ Imperial high-patronaged constructions, such as the great monuments in Rome and in the main towns in the provinces 80,91,97,98 . Among them there is also Aquileia, as coarse pumices and lavas from the Phlegraean Fields and Somma-Vesuvius were used to lightweight the opus caementicium vaults of the Late Antique Baths of the town, which were probably built under the patronage of the Imperial family 55 .…”

“…This may indicate that the circulation of the material was still limited at the time, possibly because of high transportation charges, but its distribution in Aquileia did not increase even in later centuries. Indeed, in the analysis of more than 300 mortar samples from public and private buildings of the town 54 the occurrence of the Neapolitan pozzolans was detected only in the preparation mortars of the theatre's orchestra and hyposcaenium, together with the aforementioned opus caementicium vaults of the Late Imperial baths.…”

“…The aggregates used in these mortars have a local provenance, as their petro-mineralogical nature corresponds with the sediments of the Isonzo-Natisone-Torre fluvial networks 52 , regularly employed as raw aggregate in mortars [53][54][55][56] and wall-paintings 57,58 of Roman Aquileia.…”

Aquileia and its urban development in the light of recent and ongoing research

“…The thermal building had huge proportions (around 20,000 m 2 ), oversized for the needs of Aquileia, and, with the quality of its construction technique (Dilaria et al 2022) and the opulence of its decorations, mosaic pavements and marble coverings, it reveals the aim of the Imperial patron to use it for propaganda (Cadario 2023). The Great Baths (Fig.…”