Almost two thousand years after the eruption of Vesuvius that destroyed Pompeii and Herculaneum, certain periods of the history of Naples have just been reconstructed. Until now, historians and archaeologists had wondered about the impact of this volcanic eruption on the Aqua Augusta aqueduct which supplied Naples and neighboring cities with water. Recent geochemical analyses have made it possible to directly link the lead in the water pipes of the period with that trapped in the sediments of the old port of Naples. Results clearly show that the hydraulic network had been destroyed by the eruption of Vesuvius in AD 79 and that it took around fifteen years to replace it.
These findings are the subject of an article published in the journal PNAS on May 16 2016 by the laboratory Archéorient -- environnements et sociétés de l'Orient ancien (CNRS/Université Lumière Lyon 2) and Laboratoire de géologie de Lyon: Terre, planètes et environnement (CNRS/ENS Lyon/Université Claude Bernard Lyon 1), in collaboration with University of Glasgow, University of Southampton and Universita' degli Studi di Napoli Federico II.
During the construction of a new underground line, archaeological excavations were carried out in the ancient, long-buried port of Naples. They made it possible to study a six-meter thick deposit of sediment layers accumulated in the port over centuries. The geochemical analyses of these sedimentary deposits showed that the water of the port had been contaminated over the first six centuries AD with lead from the water circulation system of Naples and neighboring towns. This lead, which was the main component of the water pipes, dissolved into the water and spread into fountains and supply points before finally running into the port. Studying the isotopic composition of this element, i.e., the proportion of different lead isotopes in the sediments makes it possible to retrace events that took place two thousand years ago.
The analyses mainly revealed two distinct lead isotopes, before and after the eruption of Vesuvius in 79 AD. They prove that the vast water supply system of the bay of Naples was destroyed by the volcanic eruption and reconstructed using lead from one or more different mining areas. This sudden change in the lead signal, which occurred about fifteen years after the eruption, suggests that the Romans repaired the aqueduct and water pipes over a relatively short period of time.
This study also helps reconstruct the different phases of Naples' urban development in the 1st to 5th centuries AD. Lead is increasingly present in the sediments, suggesting an expansion of the hydraulic network or its intensification in the areas already supplied. From the beginning of the 5th century, however, the sediments are less contaminated, revealing that the water supply suffered further damage from barbarian invasions (the aqueduct was seized so as to cut off the town's water supply), new eruptions of Vesuvius in 472 and 512, epidemics or the city's economic and administrative collapse.
This interpretation of metal pollution in ancient port sediments, which makes it possible to retrace the history of a region, could be applied to other civilizations and geographical areas. In ongoing debates about the Anthropocene, this approach could provide new perspectives on the dynamics of human footprint on the environment.
 This laboratory is part of the Maison de l'Orient et de la Méditerranée Jean Pouilloux, a research federation on ancient societies
 This work received logistic support from Soprintendenza Speciale per I Beni Archeologici di Napoli e Pompei and financial support through the ANR Jeune Chercheur program and the European Research Council ("Rome's Mediterranean Ports" program -- 339123).
 A chemical element can exist in different forms known as isotopes, which differ in their nuclear mass.
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