Integrated geophysical surveys for the knowledge of a monument of Lecce: the sixteenth-century fortifications


ACTA IMEKO 
ISSN: 2221-870X 
October 2018, Volume 7, Number 3, 73 - 78 

 

ACTA IMEKO | www.imeko.org October 2018 | Volume 7 | Number 3 | 73 

Integrated geophysical surveys for the knowledge of a 
monument of Lecce: the sixteenth-century fortifications 

Giacomo Di Giacomo1, Lara De Giorgi1, Immacolata Ditaranto1, Giovanni Leucci1, Ilaria Miccoli1,  
G. Scardozzi1 

1 Institute for Archaeological and Monumental Heritage – National Research Council (IBAM-CNR) c/o Campus Universitario, Lecce, Italy 

 

 

Section: RESEARCH PAPER  

Keywords: Archaeology; Geophysics; Measurements; Ancient walls 

Citation: Giacomo Di Giacomo, Lara De Giorgi, Immacolata Ditaranto, Giovanni Leucci, Ilaria Miccoli, G. Scardozzi, Integrated geophysical surveys for the 
knowledge of a monument of Lecce: the sixteenth-century fortifications, Acta IMEKO, vol. 7, no. 3, article 12, October 2018, identifier: IMEKO-ACTA-
07 (2018)-03-12 

Section Editor: Sabrina Grassini, Politecnico di Torino, Italy 

Received March 11, 2018; In final form August 16, 2018; Published October 2018 

Copyright: © 2018 IMEKO. This is an open-access article distributed under the terms of the Creative Commons Attribution 3.0 License, which permits 
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited 

Corresponding author: Giovanni Leucci, giovanni.leucci@cnr.it  

 

1. INTRODUCTION 

In 2014 and in 2015 integrated geophysical surveys were 
carried out outside the northern section of the sixteenth-century 
city walls of Lecce by a team of researchers of the Laboratory of 
Geophysical applied to the Archaeological and Monumental 
Heritage and the Laboratory of Ancient Topography, 
Archaeology and Remote Sensing of CNR-IBAM in Lecce. The 
investigations were carried out in cooperation with the chair of 
the Medieval Archaeology of the University of Salento, 
responsible for archaeological excavations aimed at studying the 
ancient remains inside and outside the sixteenth-century city 
walls. The investigations were performed during the massive 
restoration works promoted by the Municipality of Lecce and 
aimed at enhancement of value of this section of the city walls, 
including the reconstruction of the original aspect of the 
fortifications and the external moat. 

 

The main goal of the geophysical surveys was to identify the 
large moat outside the city walls, excavated in the rocky bank 
(quite close to the surface) and filled with soil probably in the 
18th century or at the beginning of the 19th century. In 
particular, the geophysical measurements were based on 
Ground-penetrating Radar (GPR) and Electrical Resistivity 
Tomography (ERT) techniques; in this paper, the main results of 
GPR prospecting are presented. First results were presented at 
the Third International Conference on Metrology for 
Archaeology [12]. 

Geophysical survey allowed the researchers to determine the 
direction, width and depth of the sixteenth-century moat. Hence, 
the excavation activities in the area immediately outside the 
fortifications were performed according to the results of the 
geophysical prospecting, which highlighted also other anomalies 
related to more ancient remains identified during the 

ABSTRACT 
Within the project for the restoration of the northern section of the sixteenth-century city wall of Lecce, CNR-IBAM carried out 
geophysical surveys aimed at the study and the reconstruction of the fortifications system. In particular, the investigations focused on a 
wide band of land outside the two bastions at the northern far end of the fortifications. The integrated use of GPR and ERT systems has 
allowed to detect anomalies related to the main ditch outside the city wall and to characterize the rocky bench in which it was excavated; 
at the time of the surveys, this ditch was still buried, and the results of the measurements have guided its excavations. Moreover, the 
investigations have allowed to identify also other possible ditches or quarries and more ancient structures, which subsequent 
archaeological excavations have dated at the Roman period. Moreover, geophysical surveys highlighted the presence of modern walls, 
corresponding with the foundations of the stadium constructed in the first half of the 1900s close to the fortifications. So, geophysical 
investigations were very important since they allowed not only to direct the archaeological excavations, but also because they allowed 
to formulate some hypotheses on the ancient topography of the not excavated area.  

mailto:giovanni.leucci@cnr.it


 

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archaeological excavations as a Medieval dich and a Roman road. 
At the same time, geophysical surveys have highlighted 
numerous anomalies related to the recent history of the 
investigated area, where in 1920s a stadium was built. Lastly, the 
investigations were also very important since they allowed not 
only to direct the archaeological excavations, but also to 
formulate some hypotheses on the ancient topography of the not 
excavated area. 

2. STUDY AREA 

The study area is located at the northern end of the city walls 
of Lecce built in sixteenth-century, partially retracing the 
previous fortifications of the Messapian and Medieval periods 
(Figure 1). These works were encouraged by the King Carlo V 
and executed by architect Gian Giacomo dell’Acaya, starting 
from 1542. This intervention also included the adaptation of the 
northern end of the defensive system; in fact, this sector was 
perhaps initially constituted by a lance-shaped bastion, then 
replaced by a more effective polyorcetic solution consisting of an 
advanced defensive-work with double bastions tenaille-shaped 
(nowadays called bastions of S. Francis) [1]. The imposing 
defensive system was completed by a deep moat, about which all 
traces have been lost due to a subsequent filling.  
Therefore, the main goal of the geophysical investigations, in line 
with the project of recovery and valorisation of the city walls, was 
to identify the main moat of this sector of the defensive system 
and other possible anomalies that could contribute to increase 
the knowledge of the ancient topography of the area and its 
transformations over the centuries. At this regard and in order to 
correctly interpret the data obtained from geophysical surveys, 
historical maps and historical aerial photographs have been 
acquired and studied. The aim was to reconstruct the recent 
history of the investigated area and to document the presence of 
modern structures nowadays demolished (at this regard see also 
the previous researches carried out in Lecce [2,3]). Specifically, 
while in the “Pianta della città di Lecce” drawn by Michele Astuti 
in 1882 the area immediately outside the city walls appeared as 
an open space, in an aerial photo of 1947 it was partially occupied 
by modern edifices. In particular, two buildings were immediately 
to the north of the double bastions and the structures of the 

“Campo polisportivo Achille Starace”, built in 1924, were in the 
area immediately to the west of this stretch of city walls. These 
structures were used until 1966; afterwards, they progressively 
dropped in disuse and finally were dismantled to use the area, in 
the last decades, as a parking. 

 The investigated area involved a stretch of about 500 m of 
the city walls and a surface of approximately 1.8 hectares, which 
was entirely covered by the GPR measurements. Profiles and 
time slices were positioned using a Differential GPS (DGPS) 
system and georeferenced on the large-scale archaeological map 
of Lecce. 

3. GEOPHYSICAL MEASUREMENTS 

Geophysical survey was undertaken in five areas using both 
Ground-penetrating Radar (GPR) and Electrical Resistivity 
Tomography (ERT) techniques.  

3.1. GPR data analysis 

For GPR measurements a Ris Hi mod georadar system with 
dual band 600 MHz-200 MHz antennae was used. 

The GPR data have been gathered with transect with a 
variable distance (0.5m and 2.0m) between any two adjacent 
measurement lines, and the data have been processed by making 
use of the GPRSLICE code [7]. Particularly, the processing has 
consisted in zero timing, background removal, gain variable vs. 

 

Figure 1. Lecce, the northern side of the sixteenth-century city walls with the 
Bastion of St. Francis. In yellow the investigated area. 

 

Figure 2. Lecce, area of the St. Francis Bastions: GPR time slices (129-144 cm 
depth; 200 MHz) georeferenced on 2010 Google Earth satellite image. 

 

 

Figure 3. Lecce, area of the St. Francis Bastions: GPR profiles (600 MHz 
antenna above, 200MHz antenna below) acquired in a perpendicular way to 
the walls. 



 

ACTA IMEKO | www.imeko.org October 2018 | Volume 7 | Number 3 | 75 

the depth and Kirchhoff migration [8]. The dielectric constant 
has been retrieved from the diffraction hyperbolas [8]. 

The analysis of the GPR data pointed out (Figure 3): the 
presence of an interface, denominated “base rock”, located 
between 3.0 m and 4.0 m in depth; the presence of numerous 
anomalies that represent a cut in the bed rock; such anomalies 
are due to the probable presence of the limit of the moat; other 
reflection events could be related to the probable presence of 
archaeological structures. 

In Figures 2, 4 and 6, the horizontal slices at the respective 
estimated depths of 129-144 cm (Figure 2), 147-162 cm (Figure 
4), and 135-170 cm (Figure 6) are represented. They show the 
most interesting results among those gathered in the investigated 
areas. 

 

 

 

Figure 5. Lecce, sixteenth-century city fortifications. Schematic 
georeferencing of GPR profiles: A, sixteenth-century moat; B, Medieval moat. 
In green the bedrock. 

 

Figure 6. Lecce, sixteenth-century city fortifications. GPR time slices (135-
170 cm depth; 200 MHz antenna) georeferenced on 2015 Google Earth 
satellite image. A, anomalies related to the stands of old stadium; B, 
anomalies probably related to the building of changing room of the stadium.  

Figure 4. Lecce, sixteenth-century city fortifications: GPR time slices (147-162 
cm depth; 600 MHz antenna) georeferenced in large scale map of Lecce. In 
yellow the layout of the “Campo Polisportivo Achille Starace”. 

 

Figure 7. Lecce, ERT measured area. 



 

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3.2. ERT data analysis 

The surveyed area is approximately 12000 m2 (Figure 7). In 
order to investigate below the whole area, special ERT arrays 
were used. The electrodes are distributed in such a way as to 
surround the area [9, 10, 11]. A dipole–dipole equatorial-parallel 
array was used. Initially, a 2D survey is conducted along each 
perpendicular line or transect. In the next step, the current 
electrodes remain at the end of one line, while the potential is 
moved along the line. Then, the current electrodes move one 
electrode position and the potential electrodes move as 
previously described. The process is repeated until the current 
and potential electrodes cover the L geometry. This sequence of 
observations produces a series of apparent resistivity 
observations towards and beneath the central portion of the 
array (Figure 7).  

Resistivity data were collected using a Syscal Kid switch 
device (IRIS Instruments, France) supporting 24 electrodes with 
two reels of 55 m long connecting cable and 5 m maximum 

separation between electrodes. The electrode separation for all 
arrays was 2 m. Four profiles, denoted ERT1, ERT2, ERT3 and 
ERT4, were acquired (Figure 7). A penetration depth of about 6 
m was obtained. After the data acquisition process was 
performed, the apparent resistivity data were analyzed to identify 
abnormal measurements with a high standard deviation. This is 
related to the instrument that allow to perform a number of 
measurements (in this case 6) and to calculate the mean value 
with the associated standard deviation (Figure 8). The 
investigated volume was computed using the software ErtLab 
(http://www.geostudiastier.it), which uses a Finite Elements 
algorithm. The true resistivity model computed has an 
investigation depth of 6 m, which guarantees that the inverted 
true resistivity model is deeper than the expected features. In 
order to understand the foundation depth, the analysis of 2D 
ERT data was performed.  

The 2D ERT data analysis evidenced the presence of a 
heterogeneous subsurface with resistivity values ranging from 20 

to 6000 ·m. Moreover, it is possible to note the presence of 
(Figure 9):  
- areas denoted with ‘‘A’’, with resistivity values between 100 and 

800 ·m; these values indicate the probable presence of the 
foundation walls;  
- areas denoted with “line foundation”, with higher resistivity 

values (5000-6000 ·m) that could be related to the bedrock;  
- areas denoted with “B”, with lower resistivity values (20-30 

·m) that could be related to degraded material used to fill the 
moat. 

For 3D ERT data analysis several horizontal depth slices were 
produced in order to observe the extension at depth of the 
resistivity features. Figure 9 shows the slices from 1.0 to 2.5 m in 
depth. First, it is possible to note the presence of a heterogeneous 

subsurface with resistivity values ranging from 1000 to 6000 m. 
Moreover, it is possible to note the presence of an area delimited 
by dashed dark lines with resistivity values between 1000 and 

4000  m; these values indicate the probable presence of areas 
where the moat was located.  

Figure 11 shows the slices from 1.0 to 2.5 m in depth. First, it 
is possible to note the presence of a heterogeneous subsurface 

with resistivity values ranging from 1000 to 4000 ·m. In 
addition, it is possible to note the presence of an area delimited 
by dashed dark lines with resistivity values between 1000 and 

3000 ·m; these values indicate the probable presence of areas 
where the moat was located.  

Geophysical investigations have allowed us to identify 
numerous anomalies, some closely linked to the sixteenth-
century defensive system, while others are likely to be linked to 
more ancient structures. The data relating to the characterization 
of the bedrock on which the walls were built are also very 
important, especially for the areas outside the two bastions and 
south of the north-western one. In particular, these 
measurements highlighted that the surface of the rocky bank was 
irregular and partially integrated by the foundations of the walls. 

4. THE SIXTEENTH-CENTURY MOAT  

The geophysical surveys clearly documented the sixteenth-
century moat that was excavated immediately outside the city 
walls, along the whole investigated stretch. The major anomalies 
related to the moat surrounding the fortifications have been 
highlighted thanks to the GPR profiles, which were carried out 
along the entire perimeter of the city walls and with an 
orientation orthogonal to the fortifications. 

 
Figure 8. Example of bad data. 

 
Figure 9. Lecce, 2D ERT related to ERT 2 profile.  

http://www.geostudiastier.it/


 

ACTA IMEKO | www.imeko.org October 2018 | Volume 7 | Number 3 | 77 

The measurements documented a moat between 6-8 and 10-
15 m large, and between 4.50 and 6 m deep, excavated in the 
bedrock and characterized by vertical faces (Figures 3-4); it was 
filled with soil and blocks. It is interesting to highlight that along 
L. Leo road, in the stretch south of the north-eastern bastion, the 
moat has quite the same width of the modern road; so, the 
modern buildings that flanked the eastern side of the road are 
built immediately to the east of the edge of the moat. 

Moreover, four GPR profiles measured in the area north of 
the bastions of St. Francis, beyond the moat, have highlighted 
other anomalies maybe linked to an additional moat (as frequent 
in the sixteenth-century fortifications systems); this area is under 
Bastioni Square and was not excavated. 

5. OTHER ARCHAEOLOGICAL REMAINS 

A series of other interesting anomalies was documented by 
GPR surveys a short distance from the western sector of city 
walls, in correspondence with Giaconia Palace. These are roughly 
parallel to the city walls, well visible in particular with the 600 
MHz antenna, at a depth of between 1.25 and 1.60 m (Figure 4). 
The anomalies were hypothetically attributed to an ancient 
structure about 6-7 m wide; subsequent archaeological 
excavations have clarified that this evidence was a Roman road, 
of glareata style and contained between two side walls built with 
large blocks. This road was immediately out of the city of Lupiae 
(about the urban layout of Lecce in the Roman period see [4,5,6]) 
and a stretch of it, about 140 m long, was brought to light. 

In the same area, some GPR profiles (Figure 5) documented 
anomalies linked to another moat cut in the bedrock, located a 
few meters to the west of the sixteenth-century moat; subsequent 
archaeological excavations have clarified that this evidence was a 
Medieval moat, which was 4-5 m large and partially cut the 
Roman road. It had a direction NNW-SSE quite divergent by the 

Roman road and the sixteenth-century city walls, and at its 
northern end it turned in east direction; two stretches, 
respectively 85 m (NNW-SSE orientation) and 25 m (E-W 
orientation) were brought to light.  

Lastly, again in this area west of the city walls, some GPR 
profiles have also highlighted other anomalies more to west of 
the Medieval moat, in a not excavated area; they may be linked 
to another moat (perhaps pertaining to the sixteenth-century 
fortification system) or ancient quarrying activities for the 
extraction of construction stone materials. 

6. MODERN STRUCTURES 

Lastly, in the western investigated area, GPR surveys 
documented also some structures, built in the 1920s using 
calcareous blocks and pertaining to the “Campo polisportivo 
Achille Starace”; in particular, a stretch of the eastern stand of 
the stadium (Figure 6, A) and the building of the dressing room 
(Figure 6, B) were identified. These structures were abandoned 
in 1967 and afterwards demolished. 

7. CONCLUSIONS 

The investigations presented in this paper highlight the 
importance of non-invasive geophysical systems for the research 
on cultural heritage. Geophysical prospecting, in fact, was able to 
identify numerous anomalies in the area of the northern city walls 
of Lecce, which were very useful to direct the archaeological 
excavations. In particular, the geophysical investigations have 
identified (i) the sixteenth-century moat outside the city walls, 
and the presence of (ii) a further moat and (iii) a road, which 
subsequent archaeological excavations dated respectively to the 
Medieval and Roman periods. Even some demolished structures 
of the stadium built in 1920s were identified. The use of GPR 
method also documented the characteristics of the bedrock, 
highlighting that its surface is irregular, and many detected 
geophysical anomalies are related to human activities. 
For the interpretation of GPR measurements, the positioning by 
DGPS system and the georeferencing of profiles and time slices 
on the large-scale archaeological map of Lecce were very 
important. Also, the study of the historical maps and documents 
of the 19th century and first-half of 20th century was important 
for the geophysical data interpretation. In fact, only the managing 
of all the collected and available data allows the understanding of 
the relations between the documented evidence and the correctly 
interpretation of the collected the anomalies. About the last 
matter, obviously the verification through archaeological 
excavations, which allow precise interpretation and dating, was 
very important. 

REFERENCES 

[1] V. Cazzato, M.Fagiolo, “Lecce. Architettura e storia urbana”, 
Congedo, Galatina, 2013. 

[2] G. Di Giacomo, L. De Giorgi, I. Ditaranto, G. Leucci, I. Miccoli, 
G. Scardozzi, “Integration of urban archaeology and geophysical 
prospecting: the research on the public monumental complexes 

 

Figure 10. Lecce, 3D ERT related to ERT1, ERT2 and ERT3 profiles. 

 
Figure 11. Lecce, 3D ERT related to ERT4 profile. 



 

ACTA IMEKO | www.imeko.org October 2018 | Volume 7 | Number 3 | 78 

of Lupiae (Lecce)”, in Proceedings of the 1st IMEKO 
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[4] L. Giardino, Per una definizione delle trasformazioni 
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[12] G. Di Giacomo, L. De Giorgi, I. Ditaranto, G. Leucci, I. Miccoli, 
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Proceedings of 3rd IMEKO International Conference on 
Metrology for Archaeology and Cultural Heritage, 369-373, 
ISBN: 978-92-990084-0-9. 

 

 

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