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Lead and the Roman Harbor of Portus

"[Trajan] in his wisdom and authority and devotion to the people has opened roads, built harbours, created routes overland, let the sea into the shore and moved the shore out to sea, and linked far distant peoples by trade so that natural products in any place now seem to belong to all."

Pliny the Younger, Panegyricus (XXIX)

In AD 62, Tacitus recorded that a violent storm sank two hundred ships at Portus, Rome's harbor at the mouth of the Tiber (Annals, XV.18). Begun twenty years earlier by Claudius and completed by Nero in AD 64, the port served as an anchorage for ships waiting to unload their cargo onto river barges for transport up the Tiber. But it also was exposed to the sea and may have been inundated by a tsunami, the result that year of an earthquake which devastated Pompeii (Seneca, Natural Questions, VI). It was an extraordinary maritime disaster and may have prompted Trajan to begin the construction in AD 103 of a more sheltered harbor farther inland (Suetonius, Life of Claudius, XX.3; Dio, Roman History, LX.11.1ff; cf. Juvenal, Satires, XII.75ff: "the still waters of the inner basin").

Surrounded by a complex of large warehouses and granaries, a temple and elaborate administration building and imperial residence, this hexagonal basin, which measured 1,175 feet along each side, had pierced mooring bollards for one hundred-twenty ships along its five sides. De Graauw has calculated that as many as 280 ships could be accommodated, with some being anchored in the middle of the harbor until berths became free. Trajan also constructed a canal (Canale Romano) that ran parallel to the warehouses on one side of the harbor to facilitate the transshipment of goods and alleviate silting of the river (Pliny the Younger, Epistles, VIII.17.1), which had backed up in AD 69 and caused severe flooding in Rome and the loss of its granaries (Plutarch, Life of Otho, IV.5; Tacitus, Histories, I.86).

In a 2014 study, Delile et al. sought to determine the concentration of lead isotopes in the sediment of the harbor. Core samples were taken from the channel that connected the Trajanic basin to the Claudian harbor and from the Canale Romano. It was found that "Lead isotopes in sediments from the harbor of Imperial Rome register the presence of a strong anthropogenic component....[which] demonstrate that the lead pipes of the water distribution system increased Pb contents in drinking water of the capital city by up to two orders of magnitude over the natural background." Compared to local spring water, this level was forty time greater in the early Roman empire (AD 100250), although it is "unlikely to have represented a major health risk." In part, as Delile remarks, this is because such a level represents "the final output of the water system to the Tiber, while most Roman citizens would have used drinking water that was tapped, whether legally or illegally, all along the water distribution system."

The inference is that these isotopes were deposited by the discharge of contaminated water from lead pipes (fistulae) in Rome. Although harbors are "excellent sedimentary traps," the enclosed basin at Portus may have concentrated an artificially high burden of lead in the core sample. Too, there is a confounding variable: the amount of lead already in the harbor sediment (aside from what was naturally present). The anchors of ships, for example, had lead stocks and braces, and hulls were covered in lead to protect against shipworm, sheathing that was periodically scraped to prevent fouling, which further distributed the metal. Lead ingots were carried as cargo and sometimes as ballast; lead weights were used to sound for depth and sink fishing lines; lead brailing rings were attached to lines and sails; and lead pumps emptied ships' bilges. Lead also was used to counter-balance rudder and rowing oars, and to caulk deck seams. If ships sank in the harbor, as they did, this lead, as well as the lead cooking pots and utensils onboard, were lost as well. A vast shipyard discovered in 2011 only would have added to the detritus flushed into the basin. Too, ancient lead was exceptionally pure. (Controversially, lead ingots salvaged from ancient shipwrecks have been melted and reused to shield instruments in the detection of dark matter).

In contrast to Rome, the water supply of Alexandria was conveyed, not through lead pipes, but by a canal (an inscription records it being restored by Augustus in AD 1011) that brought water from the westerly (Canopic) branch of the Nile around the southern boundary of the city. A system of conduits beneath the streets then channeled that water into underground cisterns cut into the rock (Caesar, Alexandrian War, V) where the heavy load of sediment settled, allowing the clear water to be drawn off.

Véron et al. conducted a similar study of lead isotopes in the sediment of the ancient harbor at Alexandria and found that concentrations of lead doubled during the Roman period (AD 100300), rising to 600 parts per million. It was "the highest Pb pollution ever encountered in ancient city order of magnitude higher than those measured in sediment deposits from Sidon, the only other ancient harbor to have undergone similar geochemical investigation." Such levels would seem to argue that similar lead pollution in the harbor of Portus was not causally related just to the use of lead fistulae in Rome.

The enlargement of Portus was in response to the greater supply of grain being imported to Rome, much of it being diverted from the port at Puteoli on the Bay of Naples. In a letter written shortly before his enforced suicide in AD 65, Seneca marveled at the arrival of the Alexandrian grain fleet. No matter how great the number of vessels in the harbor, he says, those sent ahead of the fleet always were conspicuous by their topsails. Whereas other ships pulled them in when the wind became too strong, depending only on their mainsails, the Alexandrians kept their topsails spread (Epistulae Morales ad Lucilium, LXXVII.1–2).

The reverse of the sesterces above commemorate the inauguration of the Portus Trajani, which was constructed about AD 103111.

References: "Lead in Ancient Rome's City Waters" (2014) by Hugo Delile, Janne Blichert-Toft, Jean-Philippe Goiran, Simon Keay, and Francis Albarède, Proceedings of the National Academy of Sciences, 111(18), 6594-6599; "Lead Use on Roman Ships and Its Environmental Effects" (2007) by Baruch Rosen and Ehud Galili, The International Journal of Nautical Archaeology, 36(2), 300-307; "Pollutant Lead Reveals the Pre-Hellenistic Occupation and Ancient Growth of Alexandria, Egypt' (2006) by A. Véron, J. P. Goiran, C. Morhange, N. Mariner, and J. Y. Empereur, Geophysical Research Letters, 33(6), L06409; Ancient Ports and Harbours (Vol. III) (2014) by Arthur de Graauw; "Recent Archaeological Survey at Portus" (2008) by Simon Keay, Martin Millett, and Kristian Strutt, Memoirs of the American Academy in Rome, Supplement, 6, 97-104.

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