Connecting Portus with Ostia: preliminary results of a geoarchaeological study of the navigable canal on the Isola Sacra

Abstract

The Roman canal, which was found using magnetometer survey in Isola Sacra (Tiber delta, Italy) in 2009 is fundamental to our understanding of the relationship between Portus and Ostia, which constitute the core of what has been defined as the « port system » of Imperial Rome. This article presents the preliminary results of a stratigraphical study of the canal in an attempt to reconstruct its morphology, phases of activity and eventual disuse. In order to achieve this, three cores were drilled at the widest point of the canal in order to analyse the deposits, while an Electrical Resistance Tomography (ERT) profile was undertaken to correlate the core sequences. The study of the results of this fieldwork suggests four periods of use. A first phase comprises a straight canal running between the Fossa Traiana (Fiumicino) and the natural mouth of the Tiber near Ostia (Fiumara Grande). A second phase is marked by a lateral mobility of the northern part of the canal, this means that the canal took a new route (CPO-2 core) while the earlier course had been sedimented (core CPO-3). This new stretch of the canal was probably disconnected upstream from the Fiumicino and filled-in with fine sediment (core CPO-2). Finally, a fourth phase of use appears with a later recut of the second phase of the canal, most likely for agricultural purposes. With a depth of between 3 and 4 meters below the Roman sea level respectively, the first two canals would have been navigable by many kinds of ancient boats but not larger vessels. These phases of canal activity are in the process of being given absolute dates.

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