Hydrographic Drone Non-Invasive Underwater Investigations: New Archaeological Discoveries in Valle Fossa di Porto (Comacchio-FE, Italy)
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Article
Hydrographic Drone Non-Invasive Underwater Investigations:
New Archaeological Discoveries in Valle Fossa di Porto
(Comacchio—FE, Italy)
Giovanna Bucci
Department of Environment and Prevention Sciences, University of Ferrara, Palazzo Turchi di Bagno,
Corso Ercole I D’Este, 32-44121 Ferrara, Italy; giovanna.bucci@unife.it
Abstract: During forensic archaeological research conducted in 2021 in the Comacchio Lagoon (FE),
we detected new data concerning the ancient local hydrography to the west of Argine Agosta, an
ancient bank, in Valle Fossa di Porto. A systematic campaign of geophysical surveys for heritage
and archaeology was conducted with a hydrographic drone equipped with a single-beam bathy-
metric sensor echo sounder, sub-bottom profiler, and side-scan sonar. In combination with the in-
direct non-invasive investigations, systematic surveys of the walkable areas were also completed.
These remote-sensing studies have relocated the River Vatrenus palaeo-watercourse, while visual
census have brought to light a system of wooden palisades with floors made of wood associated
with some scattered finds belonging to the material culture dating back to the Mediaeval and Re-
naissance periods. A preview of the results of this case study is presented here, contributing to the
reconstruction of the ancient landscape and waterscape area of the Valle Fossa di Porto.
Keywords: Comacchio; Valle Fossa di Porto; Vatrenus; archaeology; cultural heritage; remote
sensing; geophysical investigations; sub-bottom profiler; single beam; palaeo-watercourse
Citation: Bucci, G. Hydrographic
Drone Non-Invasive Underwater
Investigations: New Archaeological
1. Introduction
Discoveries in Valle Fossa di Porto In the context of the hydrographic studies of the territory of Comacchio Lagoon,
(Comacchio—FE, Italy). there was a lack of non-invasive research in the water, carried out with remote-sensing
Heritage 2023, 6, 1804–1823. technologies. Our work started this new study session of investigation; this was made
https://doi.org/10.3390/ possible as a result of the research permits received during a forensic archaeological pro-
heritage6020096 ject (co-ordinated by Project Recover Team, USA with the collaboration of who is writing)
Academic Editors: Raffaele which allowed us to use the most advanced non-invasive techniques for understanding
Martorana and Patrizia Capizzi the lagoon bed and the local stratigraphy. The permits came from Soprintendenza
Archeologia, Belle Arti e Paesaggio per la città metropolitana di Bologna e le province di
Received: 29 December 2022
Modena, Reggio Emilia e Ferrara—SABAP-BO—Archaeology sector, and from Parco del
Revised: 19 January 2023
Accepted: 2 February 2023
Delta (Research Authorization protocols below).
Published: 7 February 2023
The northern sector of Valle Fossa di Porto, between the Fosse Canal and the struc-
ture called Casone Garibaldi, had not yet been the object of specific studies and archaeo-
logical investigations since now (unlike very nearby areas which have been excavated
with extensive stratigraphic fields, since the 1970s) [1–9] (see Section 1.3 Archaeological
Copyright: © 2023 by the author.
Panorama). In addition, for this reason, the authorities in charge have welcomed the pos-
Licensee MDPI, Basel, Switzerland.
This article is an open access article
sibility of completing new non-invasive underwater geophysical investigations with
distributed under the terms and
coastal surveys, focusing our campaign on unexplored areas. The understandings of the
conditions of the Creative Commons territory, now covered by water, still not investigated, could give important results to re-
Attribution (CC BY) license late the northern sites of Comacchio (especially Valle del Mezzano and Valle Pega) with
(https://creativecommons.org/license the finds south of the Fosse canal, reaching a holistic vision of the cultural heritage related
s/by/4.0/). to the hydrography evolution.
Heritage 2023, 6, 1804–1823. https://doi.org/10.3390/heritage6020096 www.mdpi.com/journal/heritage
Heritage 2023, 6 1805
From the point of view of research planning, considering a series of preliminary sur-
veys and checks on the depth of the water, we have found that the most useful means for
carrying out remote-sensing investigations would have been a shallow draft hydro-
graphic drone. Among the various autonomous vehicles for non-invasive investigations
capable of navigating even in 30 cm-deep water, we choose the OpenSWAP—Shallow Wa-
ter Autonomous Prospector [10], a small catamaran on which several instruments could
be mounted at the same time by concentrating the scan times (see Section 2, Materials and
Methods); this means that it is equipped with an echo-side-scan sonar, single-beam, and
sub-bottom profiler, which would have allowed us to read the morphology and stratigra-
phy of the seabed, offering a diachronic complete approach.
This instrument belongs to the low-cost class of the ASV Autonomous Surface Vehi-
cles for geophysical surveys in the shallow water environment. In the ambit of the archae-
ological hydrographic investigations in eastern Emilia Romagna, this kind of surface ve-
hicle is not yet particularly widespread, despite the great versatility of this means. In this
sense, the Italian National Superintendency for Underwater Cultural Heritage is develop-
ing new guidelines for preventive archeology which also include remote-sensing investi-
gations with the combination of instruments that we have used (the work is in progress).
Similar vehicles, equipped in the same way, completed some geophysical data acquisition
in Emilia Romagna a few years ago: among the case studies, there was the Cavo Napole-
onico artificial canal (connecting the Po and the Reno rivers), a sector of the Reno river,
near Bologna, and the Comacchio Lagoon with the scope of a general morphobatimetrical
overview, dedicated mainly to environmental data acquisition [11], without going into the
merits of the possibility of interpreting the historical data and the tools for understanding
the submerged stratigraphy in relation to the cultural heritage. In addition, for this reason,
our studies are innovative.
1.1. Topographical Context
The Valle Fossa di Porto belongs to the southern sector of the Comacchio Lagoon
(FE—Italy): to the north, it borders the Fosse Canal (south of Baro Zavelea Natural Oasis);
to the west, the Provincial Road 72, called Argine Agosta—Via per Anita, extending to Via
Valle Umana (where we find the Casone Garibaldi, a historic residence, bombed in the
Second World War and rebuilt); and to the east, the Valle Fossa di Porto is partially sepa-
rated from the extension of the peninsula of Boscoforte, a palaeo-dune running from north
to south, dividing the Valle Fossa di Porto from the Valle Lido di Magnavacca (Figure 1).
Heritage 2023, 6 1806
Figure 1. Map of Valli di Comacchio IT4060002—Sito Rete Natura 2000 [12] referring to Italy: in the
red rectangle is the investigations area. To the southwest side of the lagoon is the Boscoforte dune,
with small emerging islands.
The site has undergone profound transformations, especially since the 1950s; the rec-
lamation works partially erased or hid the ancient landscape and waterscape, first with
the remodeling of banks and flooded areas, and subsequently with the construction of
artificial canals and reclamation stations for the drainage of the surrounding area so that
it could be cultivated. The arrangement of the provincial road SP 72 in an area that had
already been bombed in the 1940s and the construction of a gas pipeline covered a sector
of high archaeological interest (Figure 2).
Heritage 2023, 6 1807
(a) (b)
(c) (d)
Figure 2. Comacchio (FE), Valle Fossa di Porto c: (a) west–east panorama; (b) east–west panorama
with Casone Garibaldi; (c) north limit of the Valle Fossa di Porto: underground pipeline west of
road SP 72 (Argine Agosta) and Fosse reclamation station; (d) asphalt square with access to the
reclamation station (photo G. Bucci).
This territory by nature had already undergone several transformations: the level of
the water has changed across the centuries and the big flow of the Delta covered natural
and anthropogenic traces.
1.2. Geological Framework
The geological framework of the Valle Fossa di Porto fits into the context of the
coastal dunes and the ancient coastline, with specific reference to the Etruscan, Roman,
and Late Roman periods [13–17] (Figure 3).
Heritage 2023, 6 1808
Figure 3. Comacchio Valley and Adriatic Coast: palaeo–dunes and ancient coastal lines (black lines)
with coastal evolution (M. Stefani UNIFE) overlay mapping on Google Earth satellite image ac-
cessed on 16 January 2023.
The lithology testifies to the distributor channel deposits, such as silty clays, silts, and
very fine sands organized in decimetric layers interspersed with peaty levels and partially
decomposed organic matter. In the stratigraphy, there are mollusk shells and fine and
very fine silty sand [18].
There are coastal deposits (palaeo-shores), coastlines, and sand dunes of wind origin
made of medium and fine sands with interspersed light levels of mollusk shells, with in-
ternal levels of sandy silts and a partially decomposed organic layer. The deposits of the
brackish marsh are attested with silt, sands, and fine sands, levels of decomposed organic
substance, mixed with fine sands and clayey silts [14].
1.3. Archaeological Panorama
As mentioned, Valle Fossa di Porto is an area with diachronic archaeological evi-
dence attributable to the Roman, Late Antique, Middle Ages, and Renaissance periods.
As reported in the archaeological studies since 1971 [1], the area appeared to be scat-
tered with fragments of tiles and floor hexagons from the Roman age and erratic materials.
Excavations carried out since the 1970s brought to light a large structure, presumably
identifiable as a Roman lighthouse, to the north of our investigation area (Figure 4, site
no.1): the tower should have had control and signaling functions at the entrance to the
Fossa Augusta, an artificial canal, in the direction of Ravenna. Imperial structural remains
were identified, relating to several complexes: bricks, stone elements, fragments of plaster,
mosaic tiles, architectural elements, fragments of opus sectile, and clay pipes [2,7]. Close
to the big building, there are some remains of a Late Roman necropolis (Figure 4, site no.2).
In 2015, the ongoing excavations resumed on the brick base with a foundation on piles,
preserved with almost 2 m in height, with a square shape (side 7.42 m), already studied
in 1976 by G. Uggeri and S. Patitucci; in the same area, another brick platform was discov-
ered, aligned with the first, perhaps the access to a tall building in wood and brick and
covered in marble, partially collapsed, and stripped. A notable find is a well-preserved
parallelepiped which bears decorations in bas-relief and friezes on three faces attributable
Heritage 2023, 6 1809
to the Augustan era: bucrania surmounted by festoons, a paten, laurel leaves, and symbols
of imperial propaganda, typical of the Julio-Claudian era (site no.1 area) [19].
Figure 4. Detail of the Comacchio Lagoon from Territorio Ferrarese 1814 Map: archaeological sites
around the investigated area—yellow rectangle (https://www.patrimonioculturale-er.it/webgis/, ac-
cessed 16 January 2023). 1, Roman tower-lighthouse; 2, Late Roman necropolis; 3, the Torre Rossa,
15th cent. tower; 4, Casone Donnabona, post-Renaissance structure; 5, traces of Roman settlement;
6–7, settlements of the Early Iron Age; 8, Roman buildings; 9, Early Mediaeval wreck.
Northeast to our investigation site, we find the Torre Rossa, a 15th cent. tower (Figure
4, site no.3); to the east side, the Casone Donnabona, a post-Renaissance structure (Figure
4, site no.4); to the South, there are traces of Roman settlement (Figure 4, site no.5) on the
way of the Agosta bank, very visible on the Territorio Ferrarese 1814 Map (linking the sites
nos. 1-2-5). To the southwest side, in the Valle del Mezzano, there are anthropogenic traces
with settlements belonging to the Early Iron Age (Figure 4, sites nos.6, 7).
South of our investigation area, we find the Dosso dei Sassi, a remnant of a coastal
ridge running almost parallel, at approx. 3 km, to the inner Agosta bank (located along
site no.5, Figure 4); the site is known for the conspicuous finds of the Roman imperial age
and a villa [9]. Since 1949, repeated inspections have allowed the recovery of numerous
materials, among which two fragments of marble relief stand out, one with a wild boar
hunting scene and the other with a winged character. Marble frames and slabs of various
and precious oriental marbles, large quantities of black and white mosaic tiles, sometimes
connected to form geometric designs, hexagons bricks, including some tiles with a Solonas
stamp, and fragments of window glass, indicating the relevance of this site to a residential
complex of the imperial age [7,20]. Almost 10 km east of our study area, an Early Mediae-
val wreck was found during Years Eighty (Figure 4, site no.9).
Despite the numerous references, since today, there has been no archaeological in-
vestigation into the underwater sectors of Comacchio. This site, for sure, should have a
role of strategic importance related to natural and artificial ancient waterways, as we can
gather from the geoarchaeological studies begun during the 1970s (according to [1–16].
2. Materials and Methods
For our underwater investigations, we opted for the use of a hydrographic drone; the
deep knowledge of the geomorphological and hydrographic context determined the
Heritage 2023, 6 1810
choice. We needed an autonomous instrument that could navigate even in very shallow
waters with zero visibility, and can handle and is capable of being equipped with the main
geophysical instruments for the investigations on a seabed with soft sediment.
Our underwater non-invasive investigations used a hydrographic drone, USV Un-
manned Surface Vehicle called OpenSWAP Shallow Water Autonomous Prospector [10], a ro-
botic vehicle (overall dimensions 120 × 120 cm), zero environmental impact instrument,
low draft, controlled from a remote station by an operator who follows in real-time navi-
gation and performance of parameters. The structure of the drone is developed as a cata-
maran with a central body, and it was equipped with a single-beam bathymetric sensor
echo sounder (200 kHz), sub-bottom profiler (10–50 kHz), and side-scan sonar Tritech
StarFish 990 F (900 kHz) (Figure 5).
Figure 5. Comacchio (FE), Valle Fossa di Porto: setup of the instruments on OpenSWAP (photo G.
Bucci).
The vehicle can be driven completely automatically on pre-established routes or
manually with direct operator assistance. During the survey, the vehicle is always re-
motely controlled by an operator who will follow the navigation and the progress of the
operating parameters in real time, intervening manually in case of problems are found.
A small support boat was used for possible recovery or assistance to the autonomous
vehicle.
The positioning data have been acquired with a system of on-board software that
allows the combined management of such data and their registration simultaneously, us-
ing a GPS (the positioning was done with differential GPS with EGNOSS correction (2.5
m HDOP)).
The side-scan sonar StarFish 990 F was mounted in the vehicle and operated with a
mini-independent PC integrated into the system, with software for setting parameters and
data acquisition. This instrument is used for extreme image definition and target detec-
tion; it uses high-frequency 1 MHz acoustic ‘chirped’ pulses with a 0.3° horizontal beam
width to produce the most defined and clear images; with a 35 m range capability on each
channel (giving 70 m total swath coverage), this side-scan sonar is the ideal tool for high-
resolution surveys in inland waters.
The high-frequency single-beam echosounder (50–200 kHz) performs profiles (two-
dimensional sections) of the seabed, on the vertical of its navigation path. The system of
Heritage 2023, 6 1811
acquisition can read the depth data with centimetric precision through an automatic bot-
tom tracking algorithm, recording in SEGY format geo-referenced data.
From the post-processing of these profiles in SEG-Y format, it is possible to identify
the exact location of the bottom water–sediment interface and obtain depth data in a
timely manner, with centimeter accuracy also in very shallow water. The bathymetric
data, once processed, are saved as geo-referenced seismic SEGY files, processed, and re-
turned into profile images, with the dimensions of the backdrop provided automatically,
with automatic bottom tracking, digitization, and identification of the lagoon bed. The
data were saved in vector format (XYZ Asci text file, and DXF), with geographical co-
ordinates.
The sub-bottom profiler (10–50 kHz) made profiles (two-dimensional sections) of the
lagoon and canal beds, on the vertical of its navigation path. The system of acquisition can
penetrate the lagoon bed and reach variable depths based on the lithological nature of the
substrate. The data are recorded in geo-referenced SEGY format with a vertical resolution
of 10 cm.
The procedure of data processing begins with quality control and filtering of depth
data identified with automatic bottom tracking, processing of the acoustic profiles rec-
orded in SEGY format (standard geophysical format) with dedicated software; detection
of the bottom, and semi-automatic bottom picking where the bottom is missing tracking;
elaboration of two-dimensional seismic profiles in image format (JPG); export in ASCII
digital format XYZ file of the lagoon bed data; and the second quality control is dedicated
to delivering of the thematic maps and stratigraphic profiles. After that, the phase of iden-
tification of targets and the creation of maps with remarkable anomalies, the final geo-
referenced data are returned in the WGS84 datum, in geographic coordinates.
The remote-sensing surveys investigated a total of ~ 383.817 m2 (2 sectors: Fosse Ca-
nal and Valle Fossa di Porto, northern area—Figures 6 and 7)
Figure 6. OpenSWAP scanning in Valle Fossa di Porto, Comacchio (FE—Italy); to the right, the
Casone Garibaldi (photo G. Bucci).
Heritage 2023, 6 1812
Figure 7. Plan view of the swath completed by the Swappositioned on Google Earth satellite image
accessed on 12 March 2021 (elaboration: F. Del Bianco).
All the scans were completed with geometry as rigorous as possible, based on paral-
lel north–south swaths (Figure 7) (about remote sensing for underwater research of pal-
aeo-watercourses, see [21]).
The maximum indirect depth of investigation reached 9 m depth, below the lagoon
bed. The sub-bottom profiler was the tool that returned the greatest amount of data in
terms of the utility of interpretation of the submerged archaeological context. The geo-
physicists’ work consisted not only of the scanning phase but also of post-processing the
collected data, eliminating the multiple reflections that can occur in the lagoon environ-
ment that can obscure the signal reflected by the sedimentary layers and the anomalies.
The first processing step was developed by de-chirping the signal to obtain a more defined
reflection; and elaboration with a low-frequency pass filter at 10,000 Hz and high-fre-
quency pass filter at 1000 Hz, combining the absolute value module (ABS) and the time-
variant gain (TVG). The final post-processing phases are summarized with the following
steps: semi-manual bottom detection, slant-range correction (to remove the central hole),
de-striping, de-spiking, boundary delimitation (to remove lateral reflection), normaliza-
tion and time-variant gain, and AGC automatic gain correction. As a result of this elabo-
ration, the images became interpretable also from the archaeological point of view (see
Section 3. Results).
Visual surveys on the field were also completed, where the territory was accessible
and walkable: the visual census on itinerary of length 7360 m. The reconnaissance on foot
made it possible to document and collect some samples of archaeological finds which
were classified and documented using digital photography and dedicated forms. Cur-
rently, the finds are preserved in the deposits of the Museo Delta Antico in Comacchio.
3. Results
The geophysical investigations detected natural strata, geological elements, some
possible scattered objects, and a great sequence of stratigraphical anomalies concerning
an old river with its banks. The tool that allows us to receive more information from the
point of view of the presence of the elements relating to the submerged cultural heritage
has been, as mentioned, the sub-bottom profiler. In fact, the signals of the echo-side-scan
sonar have been strongly compromised in very shallow water by the presence of lime-
stone structures created by the polychaetes (Figure 8a). Where the water was deep, as in
the case of Fosse Canal, we detected that the bed of the waterway has been reworked
(Figure 8b).
Heritage 2023, 6 1813
(a) (b)
Figure 8. Comacchio (FE), Valle Fossa di Porto, side-scan sonar images: (a) lagoon bottom with pol-
ychaetes structures (10 m swath); (b) Fosse Canal, width 50 m, linear excavation traces in an east-
west direction (elaboration: F. Del Bianco).
The sub-bottom profiler detected a palaeo-soil at a depth of about 8.00 m, attributa-
ble, as suggested by the geologist F. Del Bianco, to the Last Glaciation [22].
From the stratigraphic point of view, a powerful layer of gray clay (US2), covered by
sandy silt (US1), emerges from the sand (US3) up to the water surface (thickness >50 cm);
on this stratum, there are postholes with a diameter of approximately 15 cm, residues of
piles (US4a and 4b) fixed together with horizontal beams on the same chronological phase
(US5). The fragments of the structure correspond to the shoreline, partially emerged, and
are subject to deterioration due to the tides and the slight wave motion generated by local
winds (Scirocco). Because of the low rainfall of the years 2020–2021 and the low tide, an
anthropogenic layer became visible during our work (Figure 9).
Figure 9. Comacchio, Valle Fossa di Porto: schematic section of a wood structure (G. Bucci).
The scanning of the sub-bottom profiler provided important information on the pres-
ence of erosive surfaces and palaeo-channels, attesting palaeo-soils (highly reflective sed-
imentary layers), with buried sand dunes. The images from the sub-bottom profiler show
how the palaeo-riverbed exceeds 8 m in depth.
The remote-sensing investigation detected the exact layout of the river Vatrenus, iden-
tified in detail following the strong discrepancy between the homogeneous filling that
characterizes it, probably linked to a large flood (Figures 10 and 11).Heritage 2023, 6 1814
Figure 10. Comacchio, Valle Fossa di Porto: markers of the palaeo-riverbed of the Vatrenus River
identified by sub-bottom profiler (yellow dots with blue line) and possible objects or small struc-
tures (red dots) (F. Del Bianco).
Figure 11. Comacchio (FE), Valle Fossa di Porto. Selection of seismo-stratigraphic images: palaeo-
watercourse of the River Vatrenus and palaeo-soils (F. Del Bianco).
The palaeo-watercourse, in the vicinity of the ancient mouth, denotes four meanders
(see Figure 9), to the south of which a para-fluvial ancient settlement attests wooden struc-
tures perhaps for fishing (see over Figures 14–15).
Elaborating on the seismo-stratigraphic data, we reconstructed a section representa-
tive of the west sector of the underwater investigations (Figure 12).Heritage 2023, 6 1815
Figure 12. Comacchio (FE), Valle Fossa di Porto, a cumulative section of the west sector (G. Bucci).
The presence of the large compact clay plateau south of the elbow meander that veers
from south to east documents the anthropization of the area between Late Antique and
Renaissance, as we can gather from the finds of material culture (see infra). The big stra-
tum occupies an area of 450 m2 ca. The anthropogenic traces are attested on 140 m2 and
they are visible mainly close to the water (Figure 13).
Figure 13. Comacchio (FE), Valle Fossa di Porto Google Earth satellite image: area of the clay plateau
with wooden findings and pottery fragments (accessed on 5 October 2021).
A complex system of postholes, as mentioned, is connected by very worn horizontal
beams: the postholes have a diameter of 15 cm; the distance between each other is 80 cm
ca and they reach a depth of about 1 m (Figures 14 and 15).Heritage 2023, 6 1816
Figure 14. Comacchio, sector south of Canale Fosse, Valle Fossa di Porto: detail of the postholes with
metric reference, captions, and orientation (photo G. Bucci).
Figure 15. Comacchio, Valle Fossa di Porto: detail of fixture poles and horizontal beams with metric
reference, caption, and orientation (photo G. Bucci).
During our surveys, we found on the coast fragments of ancient bricks and tiles (also
partially vitrified by burning), fragments of common and kitchen pottery, Roman/Late
Roman, Renaissance, and post-Renaissance pottery fragments. Notable finds include a
limestone fishing net weight, a rim with a portion of the wall of a Renaissance glass with
phytomorphic motifs, and a flat bottom of a jug (Figure 16).Heritage 2023, 6 1817
(a) (b)
Figure 16. Comacchio (FE), Valle Fossa di Porto 2021: astragal, limestone weight, 2 fragments of
amphora, 1 fragment of tile, cooking pottery, glazed pottery, graffita, 3 fragments of glazed ceramic:
(a) obverse; (b) reverse (photo G. Bucci).
The site can be traced back to scattered settlement systems with structured bank
edges and reinforced with wooden docks [23,24], a typical landscape of the ancient Delta.
To the north side of Comacchio, wooden Late Roman structures belonging to harbor
banks and small houses are attested in the district of Villaggio San Francesco; those sites
have been excavated by F. Berti, S. Gelichi, D. Calaon, E. Grandi, and who is writing, a
few years ago, documenting methodologies and construction techniques typical of the
Late Antiquity and the Early Middle Ages [25–29].
The finds of the Renaissance period probably refer to local transit, related to hunting
and fishing; the finds are found in the second layering, therefore in dispersion, simply
attesting traces of 15th- and 16th-century life.
The data coming from the structures and the ancient hydrography are more interest-
ing and they are particularly important for explaining the evolution of the local water-
courses.
4. Discussion
From the investigations carried out, new archaeological data emerge concerning the
territory’s diachronic evolution, particularly the hydrographic distribution of the fresh
waters and the settlements of the Late Antique period, near the river courses and the la-
goon.
The remains of material culture together with the wooden structures denote traces of
daily life.
Data coming from the sub-bottom profiler have made it possible to reconstruct the
course of the ancient riverbed Vatrenus and a sector of an artificial canal, the Fossa Augusta.
The Vatrenus was a river of Gallia Cispadana, one of the southern tributaries of the Padus.
It had its sources in the Apennines, flowed under the walls of Forum Cornelii (Imola), and
joined the southern branch of the Padus close to the Spineticum Ostium. The place was
maybe a harbor area at the confluence of the rivers. Plinius mentions the site and its rivers
and canals (Plinius, Naturalis historia III, 119–121—about the ancient literary sources of the
river Po—Padum and its tributaries [29,30]).
Linking the profiles to the anomalies detectable through satellite photography, we
reconstructed the palaeo-watercourse of the Vatrenus, approximately for a length of 5 km,
confirming the first hypotheses formulated by Veggiani [31–34] who recognized the an-
cient Vatrenus as a river diversion of the Santerno, running from south to north, close to
the Agosta bank, corresponding actually to the provincial road SP72 (Figure 17).Heritage 2023, 6 1818
Figure 17. Comacchio, Valle Fossa di Porto, Google Earth satellite image 4 March 2020 (accessed on
26 December 2022): palaeo-watercourse reconstruction of the Vatrenus (red line), hypothesized pro-
file—partially detected (orange line), and of the Fossa Augusta (orange straight line) (elaboration: G.
Bucci).
The studies of Balista, Bonfatti, and Calzolari [ 30] underline how important the water
supply of the Vatrenus was for the river Padus—Padovetere; the progressive and rapid aban-
donment of the ancient river branch (Vatrenus), blocked by the great floods of the Po, in-
duced the ancient inhabitants of this site to prepare a more effective north–south traffic
route to lead to the preparation of a navigable channel, located at the base of the river
bump—the Fossa Augusta—to guarantee the navigation from Ravenna to the nearest ac-
tive course of the Padum (comparisons in [33-35]). The scholars have formulated two hy-
potheses regarding the location of the Fossa Augusta: running along the Fossa di Porto
bank or parallel to the Fossa Augusta (Figure 18).Heritage 2023, 6 1819
Figure 18. The main rivers between Comacchio and Ravenna during the Roman Epoch: Padus, Erid-
anus, Vatrenus, Sinnius, Vitis, Bedesis, Sapis, Rubico, and the artificial canal Fossa Augusta (from [35]).
The 1949 IGM aerial photos, in particular the Frame: 52, Swipe: 11, Sheet: 77, Loca-
tion: 1949, Date: 11 July 1949, Elevation: 3600, Scale: 18,000, and the Map IGM F89 IV NE,
1935, Valle Lido Magnavacca, document the morphology of the river in the first half of
the last century, subsequently rectified west–east for the construction of the Fosse drain-
age complex: the residue of the river shows a meandering path in the direction of a mouth
(Figure 19).Heritage 2023, 6 1820
Figure 19. IGM Map F89 IV NE, 1935, Valle Lido Magnavacca: the study area within a red circle. To
the left, the Agosta bank, Argine Agosta; and in the center, the Fossa di Porto bank, Argine Fossa di
Porto.
5. Conclusions
The fusion of the precedent bibliography, the ancient literary sources studied by Cal-
zolari, and our non-invasive investigation offer a new interpretation of the hydrographic
system attested between the Imperial and Late Imperial Epoch.
Our investigations relocated the final fluvial sector of the river Vatrenus and have
confirmed the hypothesis of Uggeri [6,7] about the position of the Fossa Augusta, parallel
to the Argine Agosta, running (now a day underwater) close to the actual provincial road
SP 72.
Through the reconstructive section (Figure 12), from west to east, we see the deep
palaeo-riverbed with the typical alluvial traces of flooding, above the ancient dunes; the
river has been excavated quite in the center, to construct the new waterway, the Fossa
Augusta, in the stretch of the river that flowed from south to north; the margins of the cut
of the Fossa are vertical and obviously artificial, giving an unequivocal interpretation of
an anthropic artifact.
Summarizing the periodization of the studied stratigraphy, it is possible to recognize,
above the dunes belonging to the Last Glaciation (Period 1), a pre-Roman palaeo-riverbedHeritage 2023, 6 1821
definitely active until the Augustan age (Period 2); when the river lost power because of
the great floods and tended to silt up, the Fossa Augusta was dug to guarantee a navigable
route to the north (Period 3, phase 1). The waterway remains in operation until the Early
Middle Ages and probably during Late Antiquity; an arrangement of the banks and of the
emerged lands was made in correspondence with the intersection between the ditch and
the last stretch of the river; this work provided the reinforcement of bank margin and dock
construction with the wooden structures documented in these latest investigations (Pe-
riod 3, phase 2).
Remote-sensing geophysical investigations have been fundamental for the archaeo-
logical study of the submerged environment in Valle Fossa di Porto. The chance of reading
the sections up to a depth of 6–9 m gave us the possibility to understand the diachronic
evolution of the territory, offering us unprecedented results, relocating the river course
and its anthropogenic features, including artificial waterways. The use of the hydro-
graphic drone in this environment, characterized by zero visibility and very shallow wa-
ter, has proven to be the winning choice for geo-archaeological detection.
The scientific synergy between archaeologists and geologists has shown how the col-
laboration leads to results proven by stratigraphic data through historical and geological
sequences, documenting the cultural heritage across the different epochs.
The study relating to the transept investigated by us can be repeated not only over
the whole area of the Valli di Comacchio, but also in all the sites with the same geological
characteristics.
Funding: This research was funded by Project Recover Woodland CA 95695, 443 1st St., 95695
USA—https://www.projectrecover.org, accessed on 9 December 2022.
Institutional Review Board Statement: Research Authorization Protocols: Superintendence Prot.
MIC|MIC_SABAP-BO|30 August 2021|0020674-P and Parco del Delta Prot.
2021_0005952_del_17_08_2021.
Data Availability Statement: The following supporting information about the geo-archaeological
context and natural protected area can be downloaded at: http://www.archeobologna.benicul-
turali.it/fe_comacchio/faro_2015.htm, accessed on 9 December 2022; http://www.archeobologna.be-
niculturali.it/fe_comacchio/imbarcazioni_2014.htm, accessed on; https://bbcc.ibc.regione.emilia-ro-
magna.it/pater/loadcard.do?id_card=172221, accessed on 9 December 2022; http://www.parcodel-
tapo.it/it/; https://ambiente.regione.emilia-romagna.it/it/parchi-natura2000/rete-natura-
2000/siti/it4060002, accessed on 9 December 2022. Environment and cartography: https://ambi-
ente.regione.emilia-romagna.it/it/parchi-natura2000/rete-natura-2000/siti/it4060002; Geological
Map: https://www.isprambiente.gov.it/Media/carg/205_COMACCHIO/Foglio.html; Cultural Her-
itage, Emilia Romagna, Italy: https://www.patrimonioculturale-er.it/webgis/; https://geoportale.re-
gione.emilia-romagna.it/applicazioni-gis/regione-emilia-romagna (all the data were accessed on 9
December 2022).
Acknowledgments: A special thanks to the colleagues Sara Campagnari and Renata Sani
(Soprintendenza Archeologia, Belle Arti e Paesaggio per la città metropolitana di Bologna e le
province di Modena, Reggio Emilia e Ferrara—(SABAP-BO)—Archaeology sector); to Parco del
Delta Emilia Romagna; to the Team of Project Recover Patrick Scannon, Derek Abbey, Daniel
O’Brian, and Aldo Costigliolo; and to the Team of Consorzio Proambiente Fabrizio Del Bianco,
Francesco Riminucci, and Gianluca Zuffi.
Conflicts of Interest: The authors declare no conflict of interest.
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