Integrated Methodology for Sustainable Diagnosis of Roman Monuments

Integrated Methodology for Sustainable Diagnosis of Roman Monuments

 

1. Introduction

1.1 Motivation

Cultural heritage conservation is a highly interdisciplinary field that integrates the knowledge of structural engineers, architects, art historians, and material scientists.

 

The conservation of historical structures, especially Roman monuments, extends beyond structural performance, encompassing cultural, artistic, historic, social, and scientific values. Their documentation requires both qualitative and quantitative data – often fragmented or outdated – making the task complex, particularly for monuments that have undergone centuries of transformations.

 

The study emphasizes the need for cost-effective and sustainable methodologies capable of collecting, storing, and exchanging data for preventive conservation, employing interoperable digital tools and platforms to build informative digital twins of heritage buildings.

 

1.2 Objectives

The thesis develops and implements an integrated methodology for the investigation, assessment, and conservation of Roman monuments, applied to the Crypta Balbi in Rome.

The investigation includes:

• Historical and documentary survey,
• On-site visual inspection and damage mapping,
• Photogrammetric survey,
• Non-destructive testing (sonic tomography, ambient vibration testing).

 

 

Collected data are used to generate a digital twin, composed of:

1. A Geographic Information System (GIS) model for territorial and hazard information.
2. A navigable photographic virtual model.
3. A Heritage Building Information Model (HBIM) for architectural and material data.
4. A Finite Element (FE) model for structural analysis and risk assessment.

This integrated platform supports preventive conservation and enables simulation of hazard scenarios to optimize mitigation strategies.

 

 

2. State of the Art

2.1 Digital Twin for Heritage Conservation

Heritage conservation increasingly employs digital twins – dynamic digital replicas of physical assets integrating data and models to monitor condition and simulate deterioration.

 

A digital twin supports preventive conservation by merging regular condition surveys and risk analysis to forecast degradation and optimize maintenance.

 

Building Information Modelling (BIM) provides a foundation for creating structured 3D data models. Its adaptation for heritage assets, known as Heritage BIM (HBIM), allows integration of architectural, material, and diagnostic information. HBIM differs from conventional BIM since it reconstructs the “as-is” condition of existing monuments rather than following a design process.

 

The combination of HBIM with FEM enables numerical simulation and calibration based on non-destructive testing data, allowing visualization of stresses and vulnerabilities. Studies such as Barontini et al. (2022) and Santini et al. (2021) demonstrate how HBIM models support sustainable maintenance planning, combining environmental, economic, and structural parameters.

 

Despite technological advances, challenges persist due to software costs, lack of interoperability, and limited expertise. The thesis highlights the value of open-source, cost-efficient workflows that combine GIS, HBIM, FEM, and virtual tours as scalable and accessible solutions.

 

2.2 Roman Monuments Conservation

Roman architecture developed over more than a thousand years, from the city’s foundation in 753 BCE to the fall of the Western Empire in 476 CE, and continued to influence later architectural traditions (Ramos, 2023, p.9). Its evolution is marked by technological innovation, material experimentation, and monumental construction.

 

A major breakthrough was the development of opus caementicium, or Roman concrete, which enabled the creation of vaults, domes, and large-scale infrastructures. Roman architecture covered an extensive range of building types—religious, civic, military, residential, and infrastructural—and was characterised by rational design and durable materials.

 

 

 

After the fall of the Empire, many monuments were abandoned or repurposed. Examples include the Pantheon, which was converted into a Christian church; the Theatre of Marcellus, transformed into the Palazzo Savelli-Orsini; and the Temple of Fortuna Primigenia, integrated into later palace structures. These transformations, while aiding in the survival of ancient buildings, also introduced structural changes and material heterogeneity, which complicate present-day conservation.

 

 

 

Modern conservation of Roman structures is governed by European and international standards, such as EN 16096, Eurocode 8 Part 3, and ISO 13822, which define methodologies for evaluating the condition and safety of existing buildings. These include the study of historical sources, structural systems, materials, and past interventions.

 

Due to heritage protection constraints, the use of non-destructive testing (NDT) is fundamental. Previous research (Giavarini et al., 2006; Autiero et al., 2019) has provided valuable insights into the mechanical and physical properties of Roman materials, including concrete, tuff, and brick masonry.

 

At the same time, computational tools such as the Finite Element Method (FEM) and Discrete Element Method (DEM) have been successfully applied to simulate the structural behaviour of large Roman buildings like aqueducts, baths, and temples (Faleri et al., 2018; Mordanova et al., 2017). These studies confirm the usefulness of combining experimental data with numerical modelling for the structural diagnosis of ancient monuments.

 

Ramos (2023, p.18) concludes this review by emphasising that the conservation of Roman heritage requires an integrated approach, capable of merging historical knowledge, material investigation, and structural analysis within a sustainable digital framework. This understanding serves as the conceptual foundation for the methodology developed in the following chapters.

 

 

3. Methodology

3.1 Integrated Approach for the Sustainable Diagnosis of Roman Monuments

The methodology developed by Ramos (2023, p.19) aims to provide an integrated and scalable framework for the diagnosis and preventive conservation of Roman monuments. It combines multi-scale analysis tools, ranging from territorial to architectural and structural scales, within a single interoperable digital environment.

 

 

The approach is structured around the creation of a Digital Twin, a virtual counterpart of the physical monument composed of four interconnected components:

1. Geographic Information System (GIS) model;
2. Heritage Building Information Model (HBIM);
3. Photographic Virtual Model;
4. Finite Element (FE) model.

 

Each component addresses a specific level of investigation but contributes to a unified dataset through data exchange, georeferencing, and interoperability protocols. The methodology is designed to be flexible, allowing data to be progressively refined as new information becomes available.

 

The overall workflow follows the logic of progressive knowledge acquisition, as recommended by ICOMOS and ISO 13822 standards. Initial stages focus on data collection and visual inspection, while later phases integrate numerical and analytical results.

 

 

The process begins with documentary research and visual survey, proceeds through digital data acquisition and modelling, and culminates in quantitative assessment and simulation.

 

The four models are summarised as follows:

• GIS Model: Collects and organises territorial-scale data related to geology, geomorphology, seismicity, hydrology, and anthropogenic hazards. It supports risk mapping and provides a spatial reference framework for all subsequent models.
• HBIM Model: Developed in Autodesk Revit, the HBIM provides the geometric and semantic representation of the monument. It integrates information on construction techniques, material typologies, historical transformations, and observed damages.
• Photographic Virtual Model: Built using 360° photographic panoramas and implemented through Pano2VR, this model allows intuitive visual navigation of the site. It connects spatial visualisation with documentary data and supports interdisciplinary collaboration and public dissemination.
• FE Model: Created in DIANA FEA, the FE model reproduces the structural behaviour of the monument under static and dynamic loads. It is calibrated using experimental data—particularly from sonic tomography and ambient vibration testing—to simulate realistic mechanical performance and assess vulnerabilities.

 

The interoperability among these components is achieved through data exchange protocols (e.g., .ifc, .obj, and shapefile formats), and the consistent use of georeferenced coordinate systems to ensure alignment across scales.

 

This integrated structure enables the continuous update of information, forming the digital twin of the Crypta Balbi, an evolving model capable of linking the monument’s physical condition with its digital representation.

 

 

 

4. Case study: description of the site

4.1 The Crypta Balbi Complex

The Crypta Balbi, one of the four branches of the National Roman Museum, occupies an entire block in the historical centre of Rome, bounded by Via delle Botteghe Oscure and Via Caetani. The site covers an area of approximately 7000 m² and represents a remarkable example of urban continuity from the Augustan period to the present day (Ramos, 2023, p.23).

 

Originally constructed around 13 BCE by Lucius Cornelius Balbus, the complex formed part of a larger architectural ensemble that included a theatre and an adjacent porticoed courtyard (the crypta). Over the centuries, the site experienced multiple phases of transformation – medieval occupation, Renaissance palazzo construction, and modern archaeological excavation – each contributing new layers to its history.

 

Today, the complex functions as a museum and archaeological site, displaying remains from Roman foundations to modern reconstructions. Its stratified structure and multi-period character make it an ideal subject for testing a multi-scale documentation and assessment methodology.

 

 

4.2 Climate

Rome is characterised by a Mediterranean climate, with hot, dry summers and mild, humid winters. According to data from the Italian Meteorological Service, the average annual temperature is approximately 16°C, with peaks around 30°C in July–August and lows near 3°C in January.

 

Precipitation is concentrated in autumn and winter, particularly in November, which records average monthly rainfall of about 115 mm. The relative humidity fluctuates between 50% and 80%, depending on the season. These climatic variations influence both environmental risks and decay processes, especially moisture-related deterioration of masonry and plaster.

 

 

4.3 Geology

The Crypta Balbi site is located within the Tiber Valley alluvial plain, composed primarily of Quaternary deposits of gravels, sands, silts, and clays overlaying marine Pliocene sediments (p.25). The total thickness of the Quaternary deposits can reach 900 m, though the upper anthropogenic layers vary between 7 and 11 m in the city centre.

 

The area is classified as geotechnically unfavourable, with poor load-bearing soils, variable stratigraphy, and the presence of underground cavities related to ancient quarries and medieval drainage tunnels. These features contribute to differential settlements and local instabilities.

 

Furthermore, satellite data indicate subsidence rates of 0.2 mm/year in the historical centre, caused by groundwater extraction, natural compaction, and anthropogenic loading.

 

The GIS model integrates this geological information through raster and vector layers obtained from the Istituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA).

 

 

 

4.4 Flood Hazard

The Tiber River historically caused frequent and severe flooding in the city of Rome. One of the most catastrophic events occurred in 1598, when water levels reached 19.56 m at Ripetta (Ramos, 2023, p.27).

 

To mitigate flooding, the Muraglioni embankments were constructed between 1876 and 1910, significantly reducing the frequency of inundations. However, the site remains exposed to pluvial flooding, caused by intense rainfall events that exceed the capacity of the urban drainage network.

 

Between 2001 and 2014, at least 26 flood incidents were recorded in central Rome, associated with heavy storms and poor maintenance of drainage systems. GIS analysis categorises the Crypta Balbi site within a medium flood hazard zone, particularly vulnerable at the subterranean and basement levels.

 

In addition to surface flooding, the rise of the groundwater table poses long-term risks, contributing to moisture ingress and salt crystallisation in masonry.

 

 

4.5 Seismicity

Although the city of Rome is considered to have low to moderate seismicity, it has historically been affected by distant earthquakes originating from the Apennine fault system. Notable events include those of 1349, 1703, and 1915, which caused varying degrees of structural damage (p.28).

 

 

 

Local geological conditions play a critical role in amplifying seismic motion. The Tiber alluvial deposits, bounded by harder Pliocene layers, act as a resonance basin, increasing ground motion intensity by approximately one degree on the Mercalli–Cancani–Sieberg (MCS) scale compared with surrounding areas.

 

According to the Italian Seismic Hazard Map (MPS04), the peak ground acceleration (PGA) expected for the city of Rome, with a 10% probability of exceedance in 50 years, is 0.12 g, corresponding to Soil Type C.

 

These conditions justify the inclusion of seismic vulnerability assessment in the integrated methodology. The GIS model stores and visualises seismic hazard data, while the FE model evaluates structural response under seismic loading.

 

 

4.6 Summary

The environmental, geological, hydrological, and seismic analyses establish the contextual framework for the Crypta Balbi digital twin. Together, they identify the main hazard factors – flooding, subsidence, and seismic amplification – that influence the monument’s conservation.

 

By integrating these datasets into the GIS model, Ramos (2023, p.29) ensures that territorial-scale risks are linked with architectural and structural diagnostics, enabling a comprehensive understanding of the monument within its urban and environmental setting.

 

 

 

5. Building Description

5.1 Historical Overview

The Crypta Balbi represents one of the most significant archaeological and architectural sites in Rome, encompassing two millennia of urban development. Constructed in 13 BCE as part of Lucius Cornelius Balbus’ theatre complex, the crypta originally served as a rectangular porticoed courtyard attached to the stage building of the theatre.

 

During the Late Antiquity, the area underwent transformations that included the partial reuse of the Roman structures for workshops and housing. In the medieval period, new buildings emerged on top of the ancient remains, creating a dense fabric of narrow streets and courtyards. Later, during the Renaissance, noble families—such as the Caetani and Mattei—constructed palaces that incorporated surviving Roman walls and foundations.

 

By the 19th century, the site had become heavily altered, with modern constructions overlaying ancient remains. Systematic archaeological excavations began only in the 1980s, revealing a complex stratigraphy from Roman to modern times. Today, the Crypta Balbi serves as both museum and excavation site, illustrating the evolution of Rome’s urban landscape from antiquity to the present (Figure 5-1, p.32).

 

 

5.2 Architectural Layout and Construction

The complex occupies an irregular block bounded by Via delle Botteghe Oscure to the north, Via Caetani to the south, Via Michelangelo Caetani to the west, and Via dei Polacchi to the east. The preserved Roman structures correspond mainly to the southern gallery of the portico, consisting of barrel-vaulted corridors built in opus caementicium faced with brickwork.

 

The plan organisation includes three main levels:

1. Basement level containing Roman foundations and service rooms;
2. Ground floor occupied by exhibition areas;
3. Upper levels composed of medieval and Renaissance masonry additions.

The construction typologies identified through HBIM documentation include:

• Roman concrete walls with brick facing;
• Stone masonry made of tuff and travertine blocks;
• Medieval brickwork in opus latericium;
• Reinforced-concrete slabs and steel structures from modern restorations.

 

The combination of ancient and modern materials results in heterogeneous mechanical behaviour, requiring careful differentiation of each component in the structural model.

 

 

5.3 Geometric Survey and Digital Documentation

A detailed geometric survey was performed using photogrammetry and 360° panoramic imaging, providing the geometric base for the HBIM and virtual models (Ramos, 2023, p.37). The model reproduces the plan and elevation geometry with a Level of Detail (LOD) 300, sufficient for structural analysis and heritage documentation.

 

All elements were modelled as parametric components in Autodesk Revit, including walls, vaults, columns, openings, and floors. The HBIM is georeferenced to the national coordinate system to allow integration with GIS datasets. Metadata attached to each element describe:

• Chronological phase (Roman, medieval, modern);
• Material type and composition;
• Construction technique;
• Conservation state;
• Damage typology and photographic references.

The HBIM thus serves as a central information repository, connecting survey data with historical documentation and analytical results.

 

 

5.4 Historical Cartography and Urban Evolution

To reconstruct the long-term transformation of the site, a series of historical maps were georeferenced and analysed in the GIS environment:

• Bufalini Map (1551) — first accurate plan of Renaissance Rome, showing the Caetani properties;
• Falda Map (1676) — depicting the evolution of the surrounding street network;
• Nolli Map (1748) — recording the block’s configuration before 19th-century demolitions;
• Military Maps (1870–1924) — documenting changes after the creation of modern streets.

These maps reveal the continuity of the urban block throughout centuries despite functional changes. The archaeological evidence confirms reuse of Roman substructures as foundations for later constructions. The GIS-based overlay highlights the persistence of original alignments within the current urban layout.

 

 

5.5 Damage Mapping and Pathology Survey

A comprehensive damage mapping campaign identified various forms of deterioration, later classified into categories and implemented in the HBIM attribute tables.

 

Main damage types include:

• Cracks: diagonal and vertical cracks affecting arches and vaults;
• Disintegration and loss of material: particularly in tuff and mortar joints;
• Moisture staining and efflorescence, due to capillary rise and condensation;
• Surface detachment of plaster and finishing layers;
• Biological colonisation, especially in the subterranean sectors.

Damage intensity was evaluated according to the ICOMOS Illustrated Glossary (2008), and spatially represented through colour-coded maps.

 

The most critical areas were located in the underground Roman vaults, where high humidity and salt crystallisation accelerate material decay. These findings were directly linked to the GIS and HBIM databases, ensuring traceability between field observations and analytical data.

 

 

6. Material characterization and testing

Material characterisation was essential to calibrate the numerical model and understand the current condition of the Crypta Balbi’s masonry structures. Due to conservation constraints, only non-destructive testing (NDT) techniques were employed. The investigation comprised sonic tomography and ambient vibration testing, both performed on representative elements of the monument.

 

6.1 Sonic Tomography

Six sonic tomography tests (T1–T6) were conducted across walls and columns to estimate internal defects and elastic modulus variations.
Wave velocities ranged from 1200–3000 m/s, indicating heterogeneous conditions; correlation with literature data (Giavarini et al., 2006) yielded elastic moduli ≈ 1.5–3 GPa.

 

6.2 Dynamic Identification

Ambient vibration testing (seven accelerometer setups) was performed using ARTeMIS software to extract modal parameters.
Dominant frequencies: 3.42 Hz, 4.88 Hz, 6.64 Hz, 7.03 Hz, 7.62 Hz; mode shapes indicate flexible response at upper timber levels and rigid-body motion in masonry cores.

 

 

Discussion of Testing Results

The combination of sonic and dynamic tests provided complementary information: sonic tomography defined local material properties and defects, while vibration testing described the global dynamic response.

 

The integration of both datasets within the HBIM–FEM framework allows for a multi-level understanding of structural performance. Areas showing low sonic velocities and high modal deformation correspond to potential weak zones, guiding future monitoring and intervention strategies (p.58).

 

 

7. Assessment

7.1 Flood Risk (Urban Scale)

A pluvial flood vulnerability matrix (after Di Salvo et al., 2018) was implemented in GIS. The museum’s façades were coded with vulnerability indices, revealing moderate susceptibility, particularly for basement areas below 10 m a.s.l..

 

7.2 Seismic Risk (Urban Scale)

Using the methodologies of Formisano et al. (2015) and Ferreira et al. (2014), global and façade vulnerability indices were computed.
Results classify the Crypta Balbi as medium–high seismic vulnerability, consistent with local amplification effects of the Tiber alluvial soils.

 

7.3 Numerical Model and Calibration (Building Scale)

A 3D FE model was created in DIANA FEA using tetrahedral and shell elements (HX24L, Q20SH).

 

Four masonry typologies were modeled: Roman concrete, stone masonry, plastered walls, and medieval infills. Calibration matched numerical and experimental frequencies, achieving MAC values > 0.85 for main modes.

 

A nonlinear pushover analysis showed progressive wall overturning mechanisms and collapse at a load factor ≈ 0.09, identifying slender columns and north–south walls as critical (Figures 8-1 to 8-4).

 

 

8. Conclusions and recommendations

The thesis successfully demonstrates a scalable integrated methodology for the sustainable diagnosis of Roman monuments.

 

Key achievements include:

• Creation of a multi-component digital twin integrating GIS, HBIM, FEM, and virtual models;
• Efficient storage and retrieval of heterogeneous historical, geometrical, and diagnostic data;
• Preliminary structural calibration and risk evaluation of the Crypta Balbi;
• Proof of concept for interoperable conservation platforms that improve collaboration among stakeholders and automate documentation updates.

 

Recommendations:

• Expand testing (e.g., thermography, radar) for deeper material characterization;
• Implement continuous monitoring for real-time data feeding into the digital twin;
• Develop shared open-access repositories for heritage documentation;
• Apply the methodology to broader Roman and post-Roman building stocks for comparative analysis and preventive management.

 

Overall Contribution

This research establishes a replicable framework for heritage conservation that balances scientific accuracy, cost-effectiveness, and sustainability. By integrating digital tools and interdisciplinary approaches, it advances the field toward a dynamic, data-driven model of preventive conservation for complex archaeological and historical monuments.