The territory of the provinces of Ferrara and Ravenna in Roman times was characterized by a 'dispersed' population, definitely influenced by land morphology, in continuous transformation. In this context the analysis of non-urban settlements is essential, through which it is possible to observe the developments linking the two territorial realities from the First Imperial Age to Late Antiquity. Between the end of the Republican Era and the beginning of the Imperial Age, the settlement pattern and productive activity of the campaigns in the region reached their greatest intensity, and around the years of Augustan principate there is a general appropriation and intensive exploitation of the agricultural territories of Cispadania. In the Augustan age, with the allocation of the classis praetoria, begins the enhancement of strategic possibilities of Ravenna. Maritime development of the city involved an extensive programme of renovation and building works, such as the construction of the fossa Augusta, intended to ensure the efficiency of the maritime basin through the new link of the city and the surrounding plain with the Po River and the territory of Ferrara. Still in the 5th century, the coastline of these two territories maintains a good economic vitality thanks to the needs of Ravenna, the capital of the Empire, through the continuous contact with the Padanian river navigation. This assertion would seem to be demonstrated not only by the huge amount of imported products, suggesting that this area is still involved in international trade, but also by the continuity of the existence of some villas that, faced with a general crisis between the end of the 2nd and 3rd centuries AD, continue to exist until the 6th-7th century AD. This is the case of the villas Agosta, Baro Zavalea, Salto del Lupo, located near the fossa Augusta, and the villas located near via del Dismano at Mensa Matelica, Osteria via Lunga, and San Zaccaria farm Danesi. This longevity is confirmed by the persistence of other Roman settlements, although it is not always easy to establish the continuity between Late Antiquity and the Early Middle Ages: Roman structures are known, for example, at the site on which the basilica of S. Maria in Padovetere was later built, and in the area of the Zuccherificio of Comacchio. The first site, in particular, lends itself to observations of an economic-political character: its foundation at the side of the Padovetere by Bishop Aurelian (519-521), attested by Andrea Agnello, and the subsequent restructuring in Justinian era, documented archaeologically, show the interest of the Church of Ravenna in the deltaic area of the Po River. With the opening of the Primaro branch and with the development of Comacchio, between the 7th and mainly 8th centuries, the importance of the area of Padovetere seems to decline and the settlement of Santa Maria begins to gravitate around the new center, with which it is connected through the Girata canal, without seeing depopulation, as it seems conceivable based on the evidence of this Church as plebs in 908. Even from these brief annotations it emerges that hydrography was fundamentally important for the populations of Late Antiquity and the Early Medieval Ages between Ravenna and Comacchio; on the other hand, at this time the same Po seems to replace the via Emilia as the main communication axis. If this is allowed, at least in a first stage, by maintaining the efficiency of the fossa Augusta, it is however still necessary to evaluate the impacts caused by the opening of a new branch, the Po of Primaro, that cuts the route of the Augustan canal. The history of the formation of the new Padanian mouth is still uncertain. The most reliable dating, 7th-8th century, could also be made in connection with the simultaneous rise of the Comacchio Emporium. Such investigations are made difficult by the fossilization of these canals that are still visible from satellite images, both multispectral and optical, and aerial photos. The analysis of remote sensing images can still provide useful elements for the definition of the ancient river course and the canals mentioned and the identification of useful elements to their contextualization. Through the analysis of archaeological remains of rural settlements and the careful reading of remotely-sensed images, particularly those from radar sensors capable of penetrating the surface with electromagnetic waves, we have sought a better understanding of the forms of population in this area in relation to hydrological changes through time. The present research falls within the framework of the activities of the Project PArSJAd-Parco Archeologico dell'alto Adriatico Crossborder Cooperation Italy-Slovenia (2007-2013), headed for the Emilia-Romagna region by the Istituto per i Beni Artistici Culturali Naturali (IBACN), to which the Dipartimento di Storia Culture Civiltà (DiSCi) participated on the basis of a specific agreement. Under the scientific direction of Fiamma Lenzi (IBACN) and Antonella Coralini (DiSCi), a survey on rural population in Roman times has started in the region. For the case-study of the provinces of Ferrara and Ravenna, the verification of documentary consistency of archaeological data was conducted by Cristina Cordoni. We would like to thank Prof. G. Gabbianelli and Dr. F. Stecchi (University of Bologna, Dipartimento di Scienze Biologiche, Geologiche e Ambientali) for the valuable information and data about the evolution of Adriatic coastline during the various historical periods..
Fig. 1. Roman villae in the provinces of Ferrara and Ravenna (basemap: topographical map 1: 200,000).
Fig. 2. Final section of the fluvial ridge of the Po di Primaro (basemap: Shuttle Radar Topography Mission 2011) (HSV Shader) and on satellite image (rielaborated from Stefani 2006). Inside the ellipse, the confluence of the Po di Primaro in the Roman riverbed of Vatreno, in the classical sources. The final section of the fluvial ridge is more evident in Google Earth Pro (from DigitalGlobe 2011), highlighted by the course of a modern road crossing the city of St. Alberto.
Fig. 3. In red the sites along the coast of Ferrara s province (basemap: mosaic of Regional Technical Maps (CTR - 1: 25,000); in blue the ancient course of the Po River; in fuchsia the course of the fossa Augusta and the Canale della Girata (for the Insula Silva, Gelichi, Calaon 2007; for the Santa Maria in Padovetere, Berti et al. 2007; for the eastern necropolis, Berti et al. 2007; for the Baro Zavalea, Corti 2007; for the Argine Agosta, Uggeri 1973).
Fig. 4. In red the sites along the coast of Ravenna s province (basemap: mosaic of Regional Technical Maps (CTR - 1: 25,000); in fuchsia the course of the fossa Augusta (for the San Severo, Maioli 1992; for the San Zaccaria, Maioli 1985; for the Mensa Matelica, Montevecchi 2003).