The 2019–20 season of fieldwork focused on several areas of the Imperial port complex, including the Claudian harbour, the Grandi Magazzini di Settimio Severo and the stretch of the river Tiber between Portus and Ostia Antica.

The new investigations of the Claudian harbour began in 2016 as part of the ERC funded Rome's Mediterranean Ports project.Footnote ¹ The aim is to understand better the moles of the artificial harbour basin which enclosed an area of approximately 200 hectares. The application of Electrical Resistivity Tomography (ERT) combined with deep coring has been successful in precisely mapping the location of the northern mole at a depth of 5 m as well as in helping to understand its construction technique (Kay et al., Reference Kay, Pomar, Keay, Strutt, Chapkanski, Goiran and Bonsall2019). The research continued in 2019 with a survey of an area further to the west at the proposed location of the Pharos (lighthouse).

Elsewhere at Portus a photogrammetry survey of the Grandi Magazzini di Settimio Severo that lies at the junction of the passageway running between the Claudian basin and the Canale di Imbocco del Porto di Traiano is recording with detailed photography the ground floor of the complex. A short season in 2019 focused upon recording the northern façade of the building which faced onto the Claudian harbour and where the 2018 Portus Fieldschool had been conducted. Following the clearance of overhanging vegetation and invasive plants by the Parco Archeologico di Ostia Antica, Footnote ² higher parts of the structure were now visible. The new plan of the building that is being developed has identified at least six structural phases extending between the later second and sixth centuries AD.

Fig. 1. The location of the northern Claudian mole at Portus and the river Tiber study area.

Over the course of the last two decades, the Portus Project has undertaken a systematic study of the hinterland around the Imperial port, using non-invasive prospection techniques to map previously unknown infrastructure such as aqueducts, roads, and canals (Keay et al., Reference Keay, Millett, Paroli and Strutt2005). Since 2007, the survey was extended to explore the area of Isola Sacra, with the aim of better understanding the landscape between the Imperial harbour complex and Ostia Antica, 3 km to the south (Germoni et al., Reference Germoni, Keay, Millett, Strutt, Keay and Paroli2011; Keay et al., forthcoming Reference Keay, Millett, Strutt and Germoni2020). The results of the survey have shown that much of the island was covered by a regular field system, while in the Trajanic period a canal was created to run between Portus and the mouth of the Tiber near Ostia. It also revealed a dense area of large warehouses on the northern bank of the river Tiber in Trastevere Ostiensis (Germoni et al., Reference Germoni, Keay, Millett, Strutt, Cébeillac-Gervasoni, Laubry and Zevi2018; Keay et al., forthcoming Reference Keay, Millett, Strutt and Germoni2020), elements of which had been revealed by earlier excavations (Zevi, Reference Zevi1972).

The investigations have now been extended to explore the body of water between Ostia Antica and Portus, using new advances in marine geophysics that allow for high-precision mapping and prospection. The earliest record of the presence of archaeological material along the lower part of the River Tiber comes from Flavio Biondo in the sixteenth century, who describes a large quantity of marble blocks close to Portus and Isola Sacra (Reference Biondo1558: 48). Little attention was paid to this part of the Isola Sacra until the 1950s with the recovery of marble from the Canale di Fiumicino (so-called Fossa Traiana) which was deposited at Ostia Antica and a later study of the southern bank (Veloccia Rinaldi and Testini, Reference Veloccia and Testini1975). There followed a period of more intense activity which revealed submerged structures, amphorae and marble in the Canale di Fiumicino and at Fiumicino itself, in an area corresponding to the sea to the west of Portus (Mocchegiani Carpano, Reference Mocchegiani Carpano1986: 63–116).

Since 1978 a large quantity of marble blocks and columns has been recovered from the riverbed of the Canale di Fiumicino in the area of Capo due Rami and extending 200 m west (Baccini, Reference Baccini1979; Reference Baccini1989) in the direction of the viaduct of the Via dell'Aeroporto di Fiumicino. A smaller group of twenty blocks of Greek marble was also discovered during agricultural work close to the Basilica di Sant'Ippolito at Isola Sacra (Pellegrino, Reference Pellegrino1990). The discovery indicated that marble arrived at Portus partially prepared and was stored in an area that has been identified as a statio marmorum on the southern bank of the Fossa Traiana (Pensabene, Reference Pensabene1994) before being loaded onto smaller vessels to be transported up the river Tiber to Rome (Pensabene, Reference Pensabene2007: 389–90).

In 1990 the then Soprintendenza per i Beni Archeologica di Ostia (SBAO) in collaboration with the Servizio Tecnico per l'Archeologia Subacquea began a programme of underwater survey at the eastern entrance to the Canale di Fiumicino in the area of Capo Due Rami (Petriaggi, Reference Petriaggi1995: fig.1). The survey discovered sections of concrete walls faced with blocks of travertine (Petriaggi Reference Petriaggi1995: 202). Following this, two projects used marine geophysical techniques to survey the Fossa Traiana and discovered further columns and blocks on the riverbed (Bosman and Casalbore Reference Bosman and Casalbore2011: 483). However, the research focused upon the morphology of the riverbed and the depositional and erosive processes, as well as its evolution (Bosman and Orlando Reference Bosman, Orlando, Guillén, Acosta-Yepes, Chiocci and Palanques2017).

The new geophysical prospection of the river Tiber and Canale di Fiumicino was conducted over a two-week period in January 2020. The first phase saw the use of a 400 kHz Norbit iWBMS multibeam echosounder with a curved array and side-mounted LiDAR for bathymetry. The system allows for increased accuracy in shallow water and coupled with the LiDAR and GNSS positioning, provides 3D data capture of nearly the entirety of the submerged and emerged area with a high degree of accuracy. The survey covered a length of 2.3 km along the Canale di Fiumicino and 3.7 km along the Tiber between Capo Due Rami and the Ponte della Scafa. Following a preliminary analysis of the data to isolate areas of archaeological interest, a Remotely Operated Vehicle (ROV) survey was undertaken to verify the results. The modified BlueROV (designed by CAP Project Management), equipped with a forward-facing 1080p high definition camera, is designed to work in riverine environments and allows long periods of immersion. Despite the strong current and low visibility (30cm), footage was collected at several points immediately in front of Ostia Antica and at several points along the Canale di Fiumicino. Whilst further verification will be necessary through diving, the survey was successful in recording new information regarding structures in the river Tiber at Ostia Antica, in particular immediately to the north of forum. The survey in the Canale di Fiumicino recorded some features that had been previously noted by earlier surveys, but was also able to record new information about isolated finds as well as record in high definition structures such as the pier bases for the ‘Pons Matidia’ Roman bridge that connected Portus with the Isola Sacra. Through the unique combination of multibeam, LiDAR and GNSS offered by the Norbit system, the submerged archaeological landscape has been recorded in precise detail and location, providing additional data for the Parco Archaeologico di Ostia Antica for the protection of this cultural heritage.