According to the ancient texts, Ostia was founded by Ancus Marcius, the fourth King of Rome. The goal was threefold: give Rome a led to the sea, ensure its supplies of wheat and salt and finally, to prevent an enemy fleet up the River Tiber. Archaeological excavations have shown that the initial urban core (castrum) back at the earliest at the turn of the 4th s. and 3rd s BC.
If large ancient buildings and the main roads have been gradually updated, the location of the river port of Ostia mouth remained unknown so far. For some, it was seen as a port lost forever. Indeed, since the Renaissance, many attempts to location of the port of Ostia were undertaken, without success. It was not until the 19th and 20th century that Italian archaeologists define an area to the Northwest of the city, near the Imperial Palace. At the beginning of the 21st century, archaeologists confirm the probable location of the basin in the northern sector, using geomagnetic instruments. But there is still no consensus on the exact location of the port and the debate remained bright.
A Franco-Italian team led by Jean-Philippe Goiran, researcher at the Archeorient Laboratory (CNRS / Université Lumière Lyon 2), so tried to permanently testing the hypothesis of a port in the North with a new geological cores. With the latest technological advances, this enables to overcome the problem of the table water that prevented traditional archaeological excavations down beyond 2 m depth.The sediment cores obtained helped to update the complete stratigraphy at a depth of 12 m and an evolution in 3 steps:
1. Layer deep, prior to the foundation of Ostia, indicates that the sea was present in the area at the beginning of the 1st millennium BC.
2. Stratum median, rich in clay-silty sediments of grey colour, which characterizes a port facies. The calculations give a depth of 6 m to the pool at the beginning of its operation, dated between the 4th and 2nd century b.c. Regarded until then as a primarily river port, which can accommodate shallow draft boats, the port of Ostia was in reality a deep pool to accommodate large marine vessels; This is what showed the depth measurement.
Mockeries, the most recent layer testifies to the abandonment of the basin in Imperial Roman times by massive accumulations of silt. With radiocarbon dates, it is possible to deduce that a succession of episodes of major floods of the Tiber River came to permanently seal the harbour basin of Ostia from the 2nd century BC BC to the first quarter of a century a.d. (and this, despite possible phases of cleaning). At that time, the depth of the basin is less than 1 m and makes all navigation impossible. These results are consistent with the speech from the geographer Strabo (58 BC – 21/25 ad) that indicates a filling of the port of Ostia by sediments of the Tiber at its time. It was then abandoned in favour of a new port complex built 3 km north of the mouth of the Tiber River, the name of Portus.
This discovery of the harbour basin of mouth in Ostia, North of the city and to the West of the Imperial Palace, will allow to better understand the relationship between Ostia, its port and the creation ex-nihilo Portus, started in 42 BC and completed under Nero in 64 a.d. This gigantic port of 200 ha will then become the port of Rome, and the largest ever built by the Romans in the Mediterranean.
Between the abandonment of the port of Ostia and Portus construction operations, the researchers estimate that nearly 25 years have passed. How Rome, capital of the world ancient and first city to reach a million people, was fed in wheat during this period? The question arises now researchers.
