Palaeoenvironmental reconstruction of the ancient harbors of Rome: Claudius and Trajan's marine harbors on the Tiber delta

During the first and second centuries AD, Emperor Claudius and then Emperor Trajan successively ordered the construction of two large harbors on the Tyrrhenian coast. Research resulted in advances in understanding the palaeoenvironments of the Portus. From a bathymetric point of view, the drillings indicate a 7/8 m depth for the main basins. Different sedimentary behaviors were observed: Claudius' basin shows sand accretion, whereas the access channel to Trajan's basin shows mud accumulation. Trajan built the second hexagonal basin because Claudius' harbor did not protect the ships from the wind and swell, and not because it was prone to rapid silting. In terms of chronology, the channel between both basins worked between the end of the 2nd century and the beginning of the 5th century, when it became completely clogged. This means that, after the beginning of the 5th century, only the junction channel (canale traverso) remained to provide an access to the Tiber and to the sea.