Petrographic-Mineralogical Characterization of Archaeological Materials from “Casa di Diana” Mithraeum Sited in the Open Museum of Ostia Antica

Claudia Scatigno,Nagore Prieto-Taboada,Aida Maria Conte,Juan Manual Madariaga,Maria Preite Martinez

doi:10.3390/cryst11070839

Claudia Scatigno, Nagore Prieto-Taboada + Show 3 more

Open Access

https://doi.org/10.3390/cryst11070839

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Abstract

Mithraea, religious Roman buildings, are very common in Italian archeological sites. There are sixteen in Ostia Antica (Rome, Italy)The poor state of conservation, due to the intrinsic environmental conditions, characterized them: they consist of open-air museums and caves simultaneously. These places of worship are characterized by the presence of heterogeneous materials, such as wall building materials (bricks and mortars) and others used for furnishings and fittings. This increases the risk of accelerated damage because the materials ‘rheology is different. Here, a full petrographic-mineralogical characterization with polarized light microscopy (PLM), X-ray diffraction (XRD), scanning electron microscope with energy dispersive X-ray (SEM-EDS) and isotopic analysis (δ13C, δ18O) is carried out on materials like travertine, marble, pumice, ceramic, and wall-building materials in “Casa di Diana” Mithraeum (Ostia Antica). Their characterization gives provenance information as well as conservation and restoration purposes. The prevalence of siliciclastic or carbonate components discriminates between red and yellow bricks, as well as different textures and minerals in the aggregate of the red ones. The mortars are typically pozzolanic, and the aggregate is mostly made up of black and red pozzolanic clasts. In the altar, apse, and aedicule, which constitute the principal place of the Mithraeum, a variety of materials used for the ornamental purpose are represented by pumices, travertine, marble, and limestone. The altar material, catalogued as marble, resulted in being a limestone coated with a white pigment.

Highlights

Roman and religious examples represent a large number. They are commonly hosted on archaeological sites [1,2] that represent open-air museums, buildings directly exposed to the outdoors and a wide variety of environmental stressors
Twenty samples, including bricks (6), mortars (4), travertine (1), pumice (3), limestone (2), plasters (2), ceramic (1) and marble (1), are sampled. All these materials come from the Mithraeum room except the ceramic sample from the dolium collected in the pre-Mithraeum
Both the red and yellow bricks were covered by decaying products like gypsum present on the surface; carbonates were more abundant in the yellow ones

Summary

Introduction

These rooms were constructed with a central aisle flanked on each side by raised seats (podia), located at the height of 50 cm above the floor [17] They remain as in the past: dark, wet, and cold, i.e., everything to recreate a particular atmosphere for the tauroctony (the killing of the bull). The walls are mainly composed of bricks and pozzolanic mortar combined through the opus caementicium technique: inner mortar and two outer bricklayers, red/orange and yellow in dispersed order The latter is a typical Roman construction technique that has revolutionized the history of construction; they consist of full masonry from the intrados to the higher floor, and the caementa (the rubble used for the voussoirs, generally pieces of stone the size of a mason’s fist) are arranged in strictly horizontal courses [19]. The building is affected by rising damp which causes carbonate and sulphate precipitation, and biological colonization as evidenced by the consumption of mortar and bricks as well as by a typical morphology of degradation by biological growth [12,13,16]

Sample’s Collection

PL1 PL2

Mortars

Conclusions