Biodiversity and conservation correlation in the case of a Roman fresco located in a semi-confined environment

The subterranean heritage includes both natural and built sites with a strong cultural and historical fingerprint, some of each being enriched with painted surfaces. These semi-confined environments shelter specific and fragile biodiversity. This paper is focused on the case of a Roman painting (2nd-3rd century AD) located in an underground archaeological site in Marino Laziale, near Rome, which was opened to the public for the first time in 2021. The painted Mithraic scene is in a good state of conservation. The methodological approach included on site and laboratory investigations aimed to screen the main biological components associated to this hypogeum monument. The observed biodiversity included heterotrophic and chemolithotrophic microorganisms, and a mesofauna composed of eutroglophile and subtroglophile species, characteristic for many subterranean environments. The ecological mechanisms and the conservation state of the work of art were analyzed for planning the best fruition practices. The aesthetic change, the possible mechanical damages induced by various organisms, and the presence of significant amounts of organic matter, represent the main risks for painting conservation. These aspects, beside the new possible risks associated with the presence of visitors, are under a constant and ongoing conservation surveillance program.