Understanding Ancient Landscapes in the Venetian Plain Through an Integrated Geoarchaeological and Geophysical Approach
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remote sensing Article Understanding Ancient Landscapes in the Venetian Plain through an Integrated Geoarchaeological and Geophysical Approach Alice Vacilotto 1, Rita Deiana 1,* and Paolo Mozzi 2 1 Department of Cultural Heritage, University of Padova, Piazza Capitaniato 7, 35139 Padova, Italy; [email protected] 2 Department of Geosciences, University of Padova, Via Gradenigo 6, 35129 Padova, Italy; [email protected] * Correspondence: [email protected] Received: 29 July 2020; Accepted: 9 September 2020; Published: 12 September 2020 Abstract: This paper reports the results of the multidisciplinary study carried out in the SE area of Ceggia, in the eastern part of the Venetian Plain. The area has been characterized, since ancient times, by numerous morphological transformation, due to the presence of lagoon and marshes, and interested by repeated reclamation. Aerial and satellite images have identified many natural and anthropogenic traces. From a geophysical point of view, electrical resistivity tomography (ERT) combined with frequency-domain electromagnetic measurements (FDEM) can help to discriminate the spatial distribution of different buried structures in conductive systems. The electrical conductivity is, in fact, directly related to the soil moisture content. The multidisciplinary approach adopted in this context, with the results obtained thanks to the contribution of aerial and satellite images, historical cartography, archaeological survey, geophysical measurements, geomorphological characterization, and 14C dating, allow us to suggest a possible interpretation of the different traces highlighted in the studied area. This approach suggests a potentially useful and replicable methodology to study similar evidence, such as along the North Adriatic coast and in broad sectors of the Po Valley. The key issue, in this kind of system, lies, in fact, in the possibility to date and compare traces visible on the surface by remote sensing, establishing their interest from an archaeological and geomorphological point of view using an integration of field measurements. At the end of this research, the classification of the different anomalies found in this hydraulic variable context, thanks to the multidisciplinary approach here adopted, suggest new hypotheses for reading the complex history of this understudied area. Keywords: aerial archaeology; landscape archaeology; electrical resistivity tomography (ERT); frequency-domain electromagnetic methods (FDEM); paleochannel 1. Introduction The study area (Figures1 and2) lies in the fine-grained, low-gradient alluvial plain of the Piave River [1,2], which is part of the Piave megafan that has been forming between the Last Glacial Maximum and the Late Holocene [3]. Fluvial activity by the Piave River (a major Alpine river with a catchment in the Dolomites) and the Livenza River (a minor Prealpine river) ended here before the Roman Age [4], so in this time, the area corresponded to a stable alluvial plain. Due to relative sea-level rise in the Middle Ages, the area became part of an extensive system of coastal wetlands that was completely reclaimed only between the 19th and the 20th century. The current topographic surface, artificially drained, is 2 m below the sea level. Remote Sens. 2020, 12, 2973; doi:10.3390/rs12182973 www.mdpi.com/journal/remotesensing Remote Sens. 2020, 12, 2973 2 of 24 Remote Sens. 2020, 12, x FOR PEER REVIEW 2 of 24 Figure 1. ((aa)) Location Location of of the the study study area. area. (b (b) )Agea Agea 2012 2012 digital digital color color orthophoto: orthophoto: 1) (1)the the study study area; area; 2) the(2) thesite site investigated investigated with with geophysical geophysical prospections prospections,, core core drilling, drilling, and and stratigraphic stratigraphic analysis analysis of of the exposed sections. In Roman times, the area of Ceggia was included in the southern southern part of of the the “ “ager” of OpitergiumOpitergium (currently Oderzo), not far from the inner edge of a sizeable lagoon-marsh extended in the vast plain between the the ancient ancient river river courses courses of of the the Piave Piave an andd Livenza Livenza (Figure (Figure 2a).2a). The The Roman Roman road road so-called so-called Via ViaAnnia Annia [5–7][5 represented–7] represented the principal the principal axis axisof communication of communication on the on eastern the eastern coast, coast, marking marking the limit the amonglimit among different different landscapes. landscapes. The Via The AnniaVia Annia crossedcrossed the theterritory territory connecting connecting the theRoman Roman centers centers of Altinumof Altinum andand IuliaIulia Concordia Concordia up upto Aquileia to Aquileia. Different. Different archaeological archaeological find findingsings during during the thetimes times in the in areathe area (Figure (Figure 2b) 2testifyb) testify to its to Roman its Roman occupation occupation [8–10 [].8 No–10 ].details No details about aboutthe population the population or the layout or the oflayout these of landscapes these landscapes are registered. are registered. The only The inform onlyation information available available is related is relatedto the so-called to the so-called stream Piavon-Canalatstream Piavon-Canalat that flows that in flows this insector, this sector, and probably and probably representing representing from fromancient ancient times times one oneof the of routesthe routes of communication of communication and and commerce commerce [11,12] [11,12 between] between OpitergiumOpitergium, the, the lagoon, lagoon, and and the the Roman harbor to the sea, the so-called Portus Liquentiae (Figure2 2a).a). In the early Middle Ages, Ceggia was once again a marginal reality or rather a borderland, if we consider that it must have been on the boundary between the Byzantine territories of the coast and the Longobard hinterland, as well as between the mainland and spaces dominated by marshy and lagoon waters. Different studies conducted in the area disagree about the position of this limit, in part recognized in the route of the Via Annia [13], according to others, it should be searched further north [14]. Of the latter opinion were the scholars who, basing on the photo-interpretation of some aerial images, recognized in some anomalies visible in Ceggia and in the neighboring territories the result of hydraulic-agricultural interventions to be related to the nearby settlement of Civitas Nova/Heraclia (a center developed starting from the 7th century AD in a Byzantine lagoon environment) (Figure 2a), though not excluding a possible Renaissance origin [14,15]. The question, therefore, is now open. At the current state of knowledge, it is not possible to establish which sphere of influence falls this area or define its ancient environmental configuration. Remote Sens. 2020, 12, 2973 3 of 24 Remote Sens. 2020, 12, x FOR PEER REVIEW 3 of 24 FigureFigure 2.2. ((aa)) Historical-topographicalHistorical-topographical map; ( (bb)) Geoarchaeological map map wi withth traces traces from from aerial aerial photographs.photographs. Legend:Legend: 1) (1) Roman Roman cities; cities; 2) (2)Early Early Medi Medievaleval towns; towns; 3) probable (3) probable site of site theof Roman the Roman port; port;4) Roman (4) Roman roads; roads; 5) main (5) watercourses; main watercourses; 6) contour (6) lin contoures with linesequidistance with equidistance 2 m; 7) southern 2 m; (7)countryside southern countrysideof Opitergium of; Opitergium8) mechanical; (8) drainage mechanical areas; drainage 9) extensio areas;n (9)of marshy-lagoon extension of marshy-lagoon areas from 17th areas century from 17thcartography; century cartography; 10) study area; (10) 11) study area studied area; (11) with area ge studiedophysical with surveys, geophysical core drilling, surveys, and core cleaning drilling, of andthe cleaningexposed ofsections; the exposed 12) paleochannels; sections; (12) 13) paleochannels; ancient lagoon (13) canals; ancient 14) lagoon loamy canals; soils; 15) (14) clayey loamy soils; soils; (15)16) clayeyarchaeological soils; (16) findings archaeological known from findings the bibliography known from [8,10] the and bibliography from data archive [8,10] and of the from SABAP data archivemodified of theby SABAPthe authors; modified 17) anth by theropic authors; aerial (17)photo anthropic lines; 18) aerial sites photo of particular lines; (18) interest: sites of A-Roman particular interest:bridge; A-RomanB-probable bridge; rustic B-probablesettlement. rusticThe geomorphological settlement. The geomorphological elements 12), 13), elements 14), and (12),15) are (13), taken (14), andfrom (15) [1]. are taken from [1]. Remote Sens. 2020, 12, 2973 4 of 24 In the early Middle Ages, Ceggia was once again a marginal reality or rather a borderland, if we consider that it must have been on the boundary between the Byzantine territories of the coast and the Longobard hinterland, as well as between the mainland and spaces dominated by marshy and lagoon waters. Different studies conducted in the area disagree about the position of this limit, in part recognized in the route of the Via Annia [13], according to others, it should be searched further north [14]. Of the latter opinion were the scholars who, basing on the photo-interpretation of some aerial images, recognized in some anomalies visible in Ceggia and in the neighboring territories the result of hydraulic-agricultural interventions to be related to the nearby settlement of Civitas Nova/Heraclia (a center developed