Archaeological Prospection of the Siena Cathedral
The hill of the Duomo and the cathedral of Santa Maria dell’Assunta in Siena (Fig.1) have been the subject of numerous researches, including quite recent ones, making it possible to clarify complex and long-term events that have led to the definition of the current situation. The main archaeological investigations conducted in this area first concerned the square in front of the Hospital of Santa Maria della Scala (Boldrini, Parenti 1991), then the hospital itself (Cantini 2005) and finally some rooms below the cathedral choir (Causarano et al. 2003).
Fig.1 – Cathedral church in Siena and the Episcopal complex.

 

The research is aimed to

1.Non-destructive prospections aimed at understanding the development of the archaeological area and the transformations of the episcopal complex.
2.Non-destructive investigations aimed at identifying cavities and pockets of moisture.
3. Geological diagnostics aimed at understanding the lithological characteristics of the stratigraphies located in correspondence with the Cathedral, the adjacent squares and the episcopal complex.
4. Integrated analysis of the complex in association with the topographical characteristics of the context

 

Filework

The acquisition of the measurements was far superior to what was proposed in the research design with substantial variations and additions made necessary by the characteristics of the context and by the need to georeference all the measurements with great accuracy. The additions are also due to the will of the working group to analyze the episcopal complex in the most systematic way.
The implementation of the project has seen a much broader diagnostic intervention aimed at an organic understanding of the transformations of the hill and the complex over time, allowing to explore the archaeological and geological stratigraphies not only of all the internal spaces, including the Baptistery of San Giovanni, but also of the external spaces with the aim of highlighting the stratigraphic relationships between the foundation subsoil of the Duomo and the neighboring spaces. We implemented the following geophysical methodologies (Fig.2):
• Ground Pentrating Radar GPR – interior of the Cathedral and Baptistery, churchyards, piazza Duomo, piazza Jacopo della Quercia, piazza San Giovanni.
• 3D electrical tomography ERT – Piazza Duomo and inside the Duomo.
• Gradiometry – Piazza Duomo.
Fig.2 – Fieldwork acquisition of geophysical and topographic measurements. From top left: measurements in Piazza Duomo with the GPR stream UP system mounted on the electric quad; GPR stream C in the churchyard of the baptistery of San Giovanni; GPR stream C in the central nave of the cathedral; installation of stakes for geoelectric measurements; execution of geoelectric measurements; magnetometry with the Foerster Ferex instrument in Piazza Duomo; GPR stream X and GPR 80 MHz in the Duomo at the wheel of fortune; phase of the Leica laser scanner survey of the piazza duomo.

In addition to what was foreseen in the design phase, for the purposes of a better knowledge of the monument, we collected the GPR measurements of all the steps of the parvises and of the staircase of the cathedral in order to avoid as much as possible discontinuity in the data and considering the topography complexity of the monument we carried out a low resolution laser scanner survey of all the areas affected by the geophysical and significant measurements in order to be able to associate the corresponding topographical and morphological articulation to each measurement (Fig.3).

Fig. 3 – Views from different perspectives of the cathedral and the episcopal complex through the representation of the point cloud Turing on and off color information.

Results

This web page has explained in a short way the characteristics of the work carried out and below we indicate by points what we believe to be the most significant general outcomes:
1. Substantial improvment of the knowledge and understanding of the historical and architectural events of the Cathedral and of the episcopal complex (confirmations, new questions, deepening of the narrative, etc.).
2. Detailed mapping of the cavities inside, outside the cathedral and the differences in floor humidity.
3. Knowledge of the geological characteristics and the relationship between them and the structural elements with the consequent possibility of drawing up a map of the criticalities and targeted diagnostic interventions on foundations and elevations.
4. Opportunity to disseminate new knowledge acquired through flyers, panels, integration into existing guides and digital products (dissemination via WEB and dedicated mobile applications, augmented reality, virtual reality, etc.).
5. Fundamental knowledge base for any form of conservation plan that can be easily integrated into CAD/GIS/BIM based management system.