ReSeMM Project – Development of a multimodal sensor network for structural and environmental monitoring. Spoke 6, Archaeological Site of Terme di Baia, Area of the Temple of Mercury
Il The project was carried out as part of the PNRR Spoke 6 public tender, Mission 4 “Education and Research” – component 2 “from research to business” – investment line 1.3 “Partnerships extended to universities, research centers, and companies for the financing of basic research projects” – research and innovation program “Changes – Creativity and Intangible Cultural Heritage,” funded by the European Union – NextGenerationEU.
The initiative involved, for the sites indicated in the call for proposals and in compliance with the instructions of the client and the local authorities responsible for protection, the design and supply of a multimodal sensor network and the creation of a cloud-based software platform, integrated with a geospatial database, capable of remotely managing the network, acquiring, storing, processing, and displaying the collected data in real time, and setting alarm thresholds.
The project, coordinated by the Department of Civil Engineering (DICIV) of the University of Salerno, with Prof. Luigi Petti as Scientific Director, also involved the Departments of Industrial Engineering (DIIN) and Cultural Heritage Sciences (DISPAC), together with the innovative start-up Modula S.r.l..
Objectives
Architectural and archaeological heritage is exposed to dangers and risks, not only natural and anthropogenic, but also climate change; added to this are the natural processes of degradation generated by the aging of materials and the variability of environmental conditions. With a view to the sustainable use of resources and heritage protection, the development of methodological approaches that promote minimal intervention and proactive maintenance plays a key role in the management process. The proposal aims to implement a model and an integrated multi-scale and multi-level monitoring network through the development of robust and expandable systems that guarantee constant monitoring of the state of health of assets, allowing the behavior of structures to be characterized, including through the implementation of BIM models to document the life cycle of structures and the development of predictive models.
The Archaeological Park of the Baths of Baia is one of the most complex and sensitive sites of Italian cultural heritage, located in a geologically active area subject to peculiar phenomena such as Phlegraean bradyseism. This is the setting for the Temple of Mercury, a monumental structure of exceptional historical and archaeological importance, characterized by a large circular hall surmounted by a hemispherical dome which, in terms of diameter and structural design, is one of the most remarkable examples of Roman thermal architecture. The building, dating back to the end of the 1st century BC and remodeled during the 1st century AD, has an internal pool originally intended for thermal functions (frigidarium), now partly buried due to vertical ground movements. The construction techniques used—sacco masonry, reticulated facing with Phlegraean tuff cubilia and pozzolanic mortar, internal cementum composed of tuff fragments and hydraulic binder—demonstrate advanced engineering know-how, as does the use of high-quality marble cladding and hydraulic signinum.
Maintenance activities for the preservation of the Temple of Mercury have become more complex over time, partly due to phenomena linked to climate change. Its proximity to the sea exposes the structure to intense wind erosion and salt aerosols; the relative humidity inside reaches high levels, especially in winter, amplifying condensation-evaporation cycles that are potentially harmful to the tuff and the remains of ancient plaster. The masonry also appears vulnerable to the presence of invasive vegetation, while the roots of the trees on the terraces above penetrate the archaeological layers, contributing to deformation and potential local instability. Added to this is the presence of groundwater in the lower basin, an element that requires particular attention as the interaction between the water substrate and porous materials can significantly affect the durability of the structure. Finally, the absence of systematic mapping of damage, historical restorations, and material conditions increases the margin of uncertainty in assessing the state of conservation.
It is precisely in response to this complexity that the project developed as part of the PNRR CHANGES program comes into play, with the aim of creating an advanced multimodal and multi-scale monitoring system for the protection of cultural heritage. The initiative, coordinated by the University of Salerno in collaboration with Modula S.r.l. and with the support of T.P.S. S.r.l., aims to build an integrated hardware-software infrastructure based on IoT technologies so that the building can be observed and interpreted as a dynamic organism, subject to constant environmental and structural changes. The approach adopted is based on the principles of proactive maintenance and minimal intervention: instead of relying exclusively on periodic checks and manual inspections, the system allows for continuous monitoring of the condition of the building, facilitating the early diagnosis of degradation phenomena and the planning of targeted interventions.
Sensor network
The technological heart of the project consists of a distributed sensor network, made up of instruments designed to operate in a restricted archaeological context. A multiparametric probe has been installed in the basin connected to the temple, capable of continuously acquiring key indicators for characterizing groundwater: water level, temperature, electrical conductivity, pH, redox potential, dissolved oxygen, and turbidity. These parameters allow the monitoring of chemical-physical processes that can affect the stability of the foundations and underground water circulation, which is particularly relevant in an area subject to geothermal variations and soil subduction-emergence dynamics.
At the same time, a dedicated environmental sensor records microclimatic variables such as temperature and relative humidity, together with the concentration of atmospheric particulate matter in its various fractions (PM1, PM2.5, PM4, PM10) and the presence of volatile compounds and nitrogen oxides. These data allow the processes of surface degradation of the masonry to be correlated with the evolution of the internal microenvironment, providing a quantitative basis for understanding the mechanisms of alteration of stone materials and finishing layers.
Summary table of sensors selected for monitoring the Mercury Time within the Archaeological Park of Baia (NA)
Data acquisition, synchronization, and transmission are managed by a fanless industrial PC housed in an IP66-rated rack, positioned to ensure operational safety and minimal visual impact on the monumental context. The multiparametric probe communicates via RS485 protocol, while the environmental sensor uses an ESP32 microcontroller as an interface for Wi-Fi data transmission. The entire system is powered by a dedicated power line, derived from a standardized panel located at the site’s ticket office and carried to the installation point via a mixed overhead-underground route of approximately 70 meters. Remote transmission takes place via a 4G/LTE network, allowing data to be uploaded to a cloud platform developed to integrate visualization, analysis, and management of customized alarm thresholds.
Planned route of the electrical trace from the point of origin of the supply to the final installation point
The monitoring system was designed with a focus on protecting the equipment and ensuring effective data collection, taking into account both the environmental conditions and the architectural characteristics of the area. The rack housing the fanless industrial PC and other components will be placed on the metal grate, raised about 10 cm above the floor. This choice prevents moisture or water stagnation from damaging the electronics and ensures stable and discreet mounting without altering the appearance or usability of the archaeological site.
Overall layout of the rack and metal support structure seen from outside the basin, showing the positioning and anchoring to the access grating
The industrial PC will be connected to the network via a 4G/LTE dongle, which will ensure continuous data transmission to the IoT platform for real-time monitoring. To obtain a stable, interference-free signal, dedicated external antennas will be installed, connected to the dongle and positioned in optimal locations to improve reception and avoid problems caused by the site structure or any obstacles.
View from inside the basin of the monitoring system configuration, highlighting the location of the multiparametric probe, the environmental sensor, and details of the support structure
As regards the sensors, a structural support anchored to the ground outside the basin and inclined inward will be used. The use of an existing upright, suitably adapted to the requirements of the system, may be considered. At the lower end, inside the basin, the multiparametric probe will be positioned, designed to work in contact with water and detect parameters useful for assessing water quality and possible structural criticalities. At the top of the upright, the environmental sensor will be installed, responsible for measuring temperature, relative humidity, and particulate matter.
The layout of the devices takes into account their different degrees of protection: the rack is IP66 certified and the probe is designed to operate in water, while the environmental sensor is not waterproof. For this reason, it will be placed in an elevated position to avoid damage in the event of a rise in water level due to either rainfall or bradyseism. Finally, the inclination of the structural support will allow the sensors to operate in the best possible conditions, ensuring accurate and reliable monitoring of the cistern.
Thanks to this architecture, the Temple of Mercury becomes an emblematic case study of the application of digital technologies to the conservation of archaeological heritage. The progressive integration of sensor data with HBIM models and Digital Twin will make it possible to simulate the behavior of the artifact in response to environmental and anthropogenic factors, offering specialists decision support based on objective indicators and predictive models. From a broader perspective, the project represents a prototype that can be replicated in other highly vulnerable contexts, contributing to the development of an advanced methodology for the protection of cultural heritage, capable of combining scientific rigor, technological innovation, and deep respect for historical material.
Diagram of the monitoring system at the Mercure Baths in the Archaeological Park of Baia, showing the devices, power supplies required, and communication protocols used