Hypogea are natural or artificial spaces located underground often of great interest from an anthropological, archeological, religious, artistic, or historic point of view. Due to their features, these environments usually present conservative problems and biological colonization could be considered as one of the main threats. The present three-year study was carried out by specialists of the Central Institute for Restoration of Rome (ICR) in the hypogeous site preserved in the Roman Archeological Museum of Positano (Positano MAR) and focused on characterizing biological alterations present on the mural paintings; setting up efficient strategies and protocols for biodeterioration control; and monitoring the efficacy of direct and indirect interventions. Patinas with different morphologies were analyzed through microscopic observations, cultural analyses and next-generation sequencing. The results proved that the alterations comprised a great variety of microorganisms forming very distinct communities, differently distributed over space and time. The main taxa represented were bacteria of phyla Pseudomonadota and Actinomycetota, fungi belonging to the genus Fusarium and Gliocladium, and algae of the genus Chlorococcum. Preservation protocols were set up considering the alterations’ composition and included the application of biocides, limiting daily temperature changes, decreasing illuminance values on painted surfaces, and the screening of natural light sources.

Preventive conservation and restoration of mural paintings in hypogean environments is a significant challenge. These types of settings are particularly difficult to manage due to their peculiar morphological and microclimatic features. Since its foundation in 1939, the Central Institute for Restoration (Istituto Centrale per il Restauro—ICR) within the Italian Ministry of Culture has been engaged in the prevention and safety of these unique cultural heritage assets. Starting from a holistic analysis of vulnerability and hazards specific to hypogean environments, this study examines the main risks and corresponding conservation strategies. Particular attention is given to the impact of residual risk on restoration decision-making, with the aim of defining logistical and operational requirements to carry out sustainable and enduring interventions in these complex settings. The compatibility and durability of restoration materials under hypogean conditions are also examined. Furthermore, thanks to funding provided by the PNRR CHANGES project, a few research directions are proposed to address unresolved issues through the investigation and assessment of innovative products and methodologies. This review aims to lay the foundation for the development of guidelines incorporating protocols for the conservation and restoration of mural paintings in hypogean contexts, with particular attention to the needs and constraints imposed by these specific environments.

Several scholars and ancient sources highlight the communicative functions of images in the ancient Roman architecture, including plant-based motifs. Among them, Corinthian capitals, usually considered overall a stylistic character, are associated mostly with the Acanthus leaves. Indeed, further neglected plants still need a more precise identification. This paper aims to carry out a systematic analysis of their botanical composition and of the potential encoded symbolic messages. Through an analysis of 83 Roman capitals, overall Corinthian (52), Corinthianising (23), and Composite (8), dated between the II century BCE to the IV century CE from the territory of Rome, we recognised 40 different plant motifs (35 of them identified), resulting in 29 families, 30 genera and 27 species. Their bottom level is characterised by few variations of botanical species, where the recurrence of Acanthu s, representing the idea of Rebirth, is the primary key to the style. The presence of emerging spikelets of Triticum sp., previously unmentioned, seems to have a recurrent and highly relevant augural role of fertility. We cannot neglect some zoomorphic associations, such as the Acanthus leaves that, at distance, show the apotropaic effect of lions’ mouths. The middle level shows the main variability of species, often hosting the presence of Asplenium scolopendrium , having an augural value. The re-flowering flowers motif, with flowers that metamorphose into other plants, recurs in Corinthianising and Composite typologies, suggesting a never-ending life. The apical level, through the abacus plants and snakes, primarily conveys the ideas of strength, light, and salvation. Graphic abstract