The geological and geo-morphological study has provided new information on the evolution of the Tiber delta during the last 4000 years circa, in particular the period between the 6th century B.C. and the 1st century A.D. In the period between the 7th – 5th centuries B.C. the Tiber flowed into the sea through two mouths situated in the zone of the Port of Claudius and Trajan. The first Roman settlement at the mouth of the Tiber should have been in this zone. Known as Ostia Tiberina it was dated according to Roman tradition to the 7th century B.C. The mouth of the Tiber moved to its present position some time before the 6th century B.C. The port was constructed in an area formed by fluvial sediment and the artificial harbours were mainly dug out of the same sediment. The basin of the port of Claudius, which goes down to 8 m below sea level, also made use of the presence of two coastal indentations which correspond to the old mouths of the Tiber. Core sampling also provided indications regarding the phases of the silting up of the port. On the basis of present geological knowledge none of the hypotheses regarding the shape and size of the port of Claudius are completely acceptable. However, the port must have had two entrances, the main one being to the south-west, the second to the north. (Carlo Giraudi, Cristiana Tata, Lidia Paroli)