Geophysics at Segni
The first phase of the work began in June 2012 with a series of targeted geophysical surveys to investigate three separate areas within the town. A combination of geophysical techniques and topographic survey were used to precisely locate features and provide a preliminary interpretation in order to guide the subsequent archaeological investigations.
Area 1: Piazza San Pietro
The aim of the survey was to identify any further features associated to the temple and its cistern complex, as well as identify and map areas undisturbed by modern services where excavation could be undertaken.
A GSSI SIR-3000 was used for the GPR survey, configured with a 400 MHz antenna mounted on a cart system with an odometer. The survey comprised 381 parallel traverses, at a distance of 25cm, for a total of 4083.46 m. The survey concentrated on the square to the south of the podium, as well as along its western edge and northern face, in a restricted space between the podium and the large circular cistern.
The survey revealed that the majority of the area has a very shallow stratigraphy, with the natural bedrock very close to the surface (30-40cm), and is heavily disturbed by modern services. However, it successful indicated a number of areas that could be investigated through excavation.
Area 2: Prato Felici
The geophysical survey combined the use of both magnetometry and GPR in order to extract the maximum possible information. The survey used a Bartington Gradiometer 601-2, with a sample interval of 0.25m and a traverse interval of 0.5m. Due to the significant slope running from west to east, the survey had to be conducted with zigzag traverses running north-south. This steep slope had a strong effect on the data collection, however several features of archaeological interest were revealed, which were subsequently targeted with the GPR survey.
A similar configuration was used for the survey to that employed for the survey of Piazza San Pietro, but with a wider traverse separation due to the difficulties presented by surveying the steep slope. The most significant features were revealed at the highest northern end of the survey area (towards the Temple of Juno Moneta).
In early March 2013 a resistance survey, using a Geoscan RM15 meter and multiplexer, was conducted in a central area of the site, further targeting some of the features revealed by the magnetometry and GPR surveys. The recorded data, which highlighted the substantial northern wall of the building, was used to position the trench in the following 2013 excavation season.
Area 3: Piazza Santa Maria
The geophysical survey was conducted using a GSSI SIR-3000 configured with a 400 MHz antenna mounted on a cart system. A total of 165 traverses of varying length were collected with a traverse separation of 0.25m. The exceptionally clear results of the GPR survey, display a sequence of high amplitude linear anomalies, which were interpreted as denoting the walls of buildings. These features appear to have similar alignments, providing insight into the historical plan of this area. Furthermore, later phases of buildings have been built on earlier structures, suggesting some level of reconstruction as well as the possible reuse of building materials.
Area 4: Cathedral of Santa Maria Assunta
In August 2013 the GPR survey was extended to inside the Cathedral of Santa Maria Assunta, with the kind permission of the Dioceses of Velletri – Segni. Using the same parameters as the previous survey in the piazza, the aim of the survey was to understand whether the structures excavated in the piazza continue in the area underneath the 17th century cathedral. The data is currently being processed and the results will be reported here soon.