Geoarchaeology of the ancient harbour bassin of Ostia, Rome, Italy

English Abstract:

For the first time we prove, by the use of corings, the location of the basin harbour of Ostia. The study of the stratigraphic sequence of Ostia basin is based on multidisciplinary geoarchaeological approach that integrate 17 radiocarbon dates obtained on 12m of stratigraphy. Three units can be distinguished: pre-harbour, harbour and post-harbour. (i) The pre-harbour is a fluvial-marine environment dated between the 9th and 8^th BC: this is the paleo-mouth of the Tiber. (ii) The base of the harbour sequence is characterized by a facies of dark grey silty clay: this is a quiet area in connection with both the river and the sea. It starts at the earliest in the middle of the 4th c. BC (360 BC) and is attested until no later than the end of the 3rd c. BC (205 BC). At that time the depth of the basin reached 6m below roman sea level. This unusual depth is very significant for the time and implies that seagoing vessels could access the basin. (iii) The summit of the harbour sequence is marked by yellow sands brought by floods of the Tiber. The protective role of the basin decreases between 165 BC and 5 AD and depth is no longer than 2.5m under the ancient marine zero. Most seagoing ships cannot access it anymore. (iv) The basin loses its function at the beginning of the imperial period because its depth was only 60 cm between 45BC and 25 AD and about 30cm between 80 and 230 AD.