Introduction
Portus was the seaport of Rome during the Roman Imperial period. The construction of the harbour began in AD 42 under the reign of the Emperor Claudius. The harbour was located about 3 km north of Ostia, along the Tyrrhenian Coast, but on the margin of the Tiber. A few hundred metres east of Portus, the natural Tiber channel curved to the south near Ostia, where it flowed into the sea (fig. 1). At the beginning of the 2nd c. AD, Emperor Trajan complemented the Claudian harbour with a second basin (Juvenal, Saturae, XII, 75-78). To date, many sedimentological and palaeoenvironmental studies have been conducted at Portus, its basins and its maritime entrances (Arnoldus-Huyzendveld, 2005; Giraudi et al., 2007; Goiran et al., 2007, 2008; Bellotti et al., 2009; Giraudi et al., 2009; Goiran et al., 2010), but much less is known about the fluvial features at Portus (Salomon et al., 2010). Inscriptions made during the reigns of Claudius (CIL XIV 85 = ILS 207) and Trajan (CIL XIV...