Archaeologists Discover River Harbor of Ostia

European archaeologists believe they have finally found the exact location of the river harbor of Ostia.

This is an aerial view of Ostia and the position of its ancient harbor. Sampling sites are shown in red (S. Keay)

Ostia was a harbor city situated at the mouth of the river Tiber, some 18 miles (30 km) to the west of Rome. It was founded by Ancus Marcius, the legendary fourth king of Rome, around 620 BC. The settlement is supposed to have aimed three goals: to give ancient Rome an outlet to the sea, to ensure its supply of wheat and salt, and finally, to prevent an enemy fleet to ascend the Tiber.

“Ancus Marcius built a city at the mouth of the Tiber, and settled it with colonists,” Marcus Tullius Cicero wrote in De Re Publica (II, 18, 33).

Archaeologists have unearthed many ancient buildings and main roads in Ostia, but the location of the river harbor remained unknown.

Some decades ago, Italian researchers proposed the possible location of the port in northwestern part of the city, near the Ostia’s Imperial Palace.

Now, the French-Italian team using a geological corer has verified the hypothetical location of the harbor. They extracted two sediment cores that show a complete 39-feet (12 m) depth stratigraphy and the evolution of the harbor zone in three stages.

The deepest stratum – before the foundation of Ostia – indicates that the sea was present in that area in the early 1st millennium BC.

A middle layer, rich in gray silty-clay sediments, points to a typical harbor. According to calculations, the basin had a depth of 21 feet (6.5 m) at the beginning of its operation. Previously considered as a river harbor that can only accommodate low draft boats, Ostia actually enjoyed a deep basin capable of receiving deep draft marine ships.

Finally, the most recent stratum, composed of massive alluvium accumulations, shows the abandonment of the basin during the Roman Imperial period. With radiocarbon dates, it is possible to deduce that a succession of major Tiber flood episodes finally came to seal the harbor of Ostia between the second century BC and the first quarter of the first century CE.

At that time, the depth of the basin was less than 3 feet (1 m) and made any navigation impossible. It was then abandoned in favor of a new harbor complex built about 2 miles (3 km) north of the Tiber mouth, called Portus. This alluvium layer fits with the geographer Strabo’s text (58 BC – 21/25 CE), who indicated the sealing of the harbor basin by sediments of the Tiber at that time.

The findings will be published in December 2012 in the Chroniques des Mélanges de l’Ecole Française de Rome.

“Ostia is harbourless on account of the silting up which is caused by the Tiber, since the river is fed by numerous small streams. Now although it means danger for the merchant ships to anchor far out in the surge, still the prospect of gain prevails; and in fact the plentiful supply of tenders which receive the cargoes and bring back others in exchange makes it possible for the ships to sail away quickly before they touch the river, or else, after being partly relieved of their cargoes, they sail into the Tiber and run inland as far as Rome,” Strabo wrote in Geographica (231-232).

The archaeologists say the discovery will help better understand the links between Ostia, its harbor and the city of Portus.

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Bibliographic information: J.-Ph. Goiran, F. Salomon, E. Pleuger, C. Vittori, I. Mazzini, G. Boetto, P. Arnaud, A. Pellegrino. Résultats préliminaires de la première campagne de carottages dans le port antique d’Ostie. Chroniques des Mélanges de l’Ecole Française de Rome, vol. 123, no. 2