If the impact that a constantly changing natural environment had on the fate of the Roman empire is now under careful scrutiny, the impact Rome had on its environment and nature has barely been considered. However, this can be measured with remarkable precision.
Roman metallurgy has left signals across northern Europe and the northern Atlantic world in the form of anthropogenic heavy metal contamination of soil, sediment, and ice. Contamination is so substantial and significant that it has been identified as the start of the Anthropocene, the period through which we are living, a discrete chapter of the Holocene, our current geological epoch. Lake beds, peat bogs, salt marshes, and ice fields produce very reliable pollution records. Cores extracted from Irish and Swedish lake beds, an Icelandic salt marsh, Faroese peat bogs, and Arctic glaciers all show the same sudden and dramatic rise in the deposition of atmospheric lead pollutants between c. 100 bc and 100. Lead is released by the smelting of a range of metallic ores, including those mined for copper and gold, tin, zinc, and silver, and from lead itself. In each location the levels of lead pollutants fall away rapidly toward 400, only beginning to rise again after 800, and not reaching Roman levels until c. 1700. In none of these locations is there any evidence for contemporary mining and smelting of metallic ores, which would have produced the contamination.
Roman-age pollution in the North Atlantic world is the direct result of fluctuations in the intensity of smelting that took place thousands of kilometers to the south, releasing into the atmosphere lead aerosol particles that were conveyed great distances within the northern hemisphere’s atmospheric transport system and deposited by precipitation. The origin of the lead in Greenlandic ice has been confirmed by geochemistry (isotope analysis). Spain was the source of up to 70 percent of the heavy metal pollution at its peak in the first century. Contamination is far greater the closer one gets to its source. In an ice core taken from the Col du Dôme glacier in the French Alps, the magnitude of lead contamination is one hundred times greater than that recorded in Greenland in the first century bc, reaching a lower peak in c. 100, before falling steadily and dramatically to its lowest point in the sixth century.
The rapid rise in atmospheric lead pollution mirrored the rise of the Roman silver denarius, the coin minted in the greatest numbers and at the peak of its fineness (at almost 98 percent silver, considered pure by the mints) from the time of Augustus in the first century. Careful analysis of Roman silver coinage supports the notion that far less silver was smelted after 100. From the reign of Nero onward, Roman silver coinage was increasingly debased. The ratio of silver to copper alloy decreased, and the amount of recycled silver used, obtained by melting down older coins, increased. The Roman silver denarius had a fixed exchange rate with the aureus, a gold coin. During the Republican period this was largely notional, but from the time of Julius Caesar gold coins were produced in greater numbers. This too appears to be reflected in the environmental record.
Gold production produced copious contamination. The largest known Roman gold-mining operation was located at Las Médulas in northwestern Spain. A sediment core extracted from a small glacial lake around thirty-five kilometers from the mines shows evidence for the first gold metallurgy at Las Médulas in around 300 bc, with a rapid increase in lead contamination from around 100 bc, a peak in c. 15 bc, and a decline to background (pre-300 bc) levels by c. 20. At the same time there were dramatic increases in both antimony and arsenic. The peak of pollution corresponds with that identified in the Greenland ice core, but the concentration of lead, being so close to the smelters, is far greater. Around 150 kilometers to the north of Las Médulas, a peat bog saw an increase in lead pollution that was thirty times greater than its local background level in c. 100, which had fallen back to the baseline by c. 500.
Silver and gold were noble and rare metals, whereas lead was a dull, base metal, the plastic of its age, and was employed in quantities and for purposes unknown before and since. It has been suggested that the Roman period should be called the “Lead Age,” an archaeological successor to the Iron Age. Lead was used extensively in Roman construction, because it is malleable and resists corrosion when in contact with air and water. Molten lead was poured around iron clamps to join column drums together and to secure marble facades to blockwork. Lead sheets and solder were used to form and seal waterproof joints. Most famously, lead was used in Roman waterworks: to form pipes that transport water at pressure, to plumb fountains and baths, for rain gutters and roofs, and as tanks to store water, including potable water, for various purposes. It has been determined that the piped water of the city of Rome may have contained up to forty times the lead of natural spring water before 250, falling to a multiple of fourteen by the year 500, as pipes became choked with scale, cracked, and failed, and the broader water system fell into disrepair.
In addition to its uses in construction and for waterworks, lead was used as a bulking agent in copper alloys, appearing in volume in later Roman copper coins. Lead tokens, and occasionally coins, were struck in great numbers. Because it was heavy, lead was used to form weights and also to give heft to bronze steelyard weights. Because it was easy to shape, lead sealings were used to secure and verify pouches, bags, and letters. Lead bungs stoppered liquids and lead labels were attached to sacks, with letters scratched into the soft metal. Its low melting point (327 degrees Celsius) and physical properties meant that lead was used in the extraction and refining of silver and gold and to give fluidity to bronze and copper for the manufacture of sculpture, vessels, and jewelry. The Roman army used lead in abundance, including lead shot. Lead compounds—“white lead” (cerussa) and “red lead” (minium)—were used as pigments in paints and cosmetics.
As a dark and dull base metal drawn from the same ore, galena, as noble shimmering silver, lead was considered chthonic and inauspicious. Thin sheets of lead formed into tablets were used for inscribing curses, which were folded and buried. Stone sarcophagi might contain a lead liner. Those who could not afford stone sarcophagi might choose to be interred in decorated lead coffins or lead-lined wooden coffins, their lids soldered shut and protective designs imprinted upon the surfaces to preserve and protect interred bodies. Lead coffins have been found in small numbers at various places across the late Roman world and in far greater numbers in Britain, where lead was naturally abundant, and the Levant, where it was not. The ubiquity of lead meant that Roman soil was polluted by it even where there is no evidence for mining or smelting. Analysis of sediments conducted at excavated sites in the modern state of Israel, where there are no known lead ore deposits, shows that the Roman occupation levels are replete with lead, unknown in earlier times and for a millennium afterward. Sediment cores taken from the harbors at Alexandria, Egypt, indicate that very little lead was present in the local environment before the foundation of the city (two to six parts per million [ppm]), followed by some use of lead in the Ptolemaic city (two hundred to three hundred ppm), spiking to around six hundred ppm in 100, followed by a steady decline to pre-Roman levels by 500. Roman levels of lead pollution are higher than those recorded in Alexandria’s modern harbor. This is not evidence for lead aerosols from smelting facilities deposited by precipitation, nor was Alexandria plumbed so extensively as Rome with lead pipes.
Rather, lead was present in abundance in the harbor itself. Lead sheathing was applied to the hulls of ships, perhaps two-thirds of all Roman ships, as protection against shipworms (teredo navalis). Some ships carried spare rolls of lead to patch and repair, while others had composite anchors and oars of wood and lead, lead sounding weights (for measuring water depth), bilge pumps with lead parts, sinkers for fishing nets and lines, and even ingenious lead braziers for safer cooking on board. Some of these fell to the seafloor, as did a great deal of lead scrapings from regular cleaning of barnacle-encrusted lead-sheathed hulls, contaminating the sediment.
Lead exposure posed a significant health risk to sailors, but that paled in comparison with the risk of living near sites where metallic ores were mined and smelted. Both Pliny the Elder and Vitruvius observed how unhealthy lead workers were. At the height of activity, before 100, many thousands of those workers were slaves, who suffered not only from lead poisoning but also from the inhalation in high concentrations of sulfur dioxide, which produces irritation and inflammation of the respiratory system and affects long-term lung function. For those who lived far from smelting facilities, lead poisoning was less common but still possible. Lead is equally toxic however it enters the body. Between 30 percent and 50 percent of inhaled lead particles remain in the body, compared with 5 to 10 percent of lead particles that are ingested.
Contrary to a popular theory, it is unlikely that many Romans ingested toxic levels of lead from their water pipes. Although lead is soluble in water, calcium carbonate deposited by hard water provided a barrier between water and lead. Moreover, calcium prevents the gut from absorbing lead. Drinking hard water transported in lead pipes did not present a major health risk to Romans, although in soft-water areas the risks were higher, and lead carbonate might form a less protective scale inside pipes. If not from their water, however, Romans contrived many additional ways to ingest and absorb lead. It was used for medicinal purposes, in cooking and for mixing sauces, and for preserving and sweetening wine. Roman saucepans manufactured from a mixture of lead and tin were used to produce reductions of must (unfermented grape juice) called, according to its concentration, sapa, defrutum, or caroenum, all full of lead. Salt was produced in lead brine pans, heated to evaporate water, before the salt was chipped and scraped away.
Flora and fauna are excellent indicators of environmental pollution, including lead contamination. Modern surveys have shown that honeybees absorb twice as much lead as drones, effectively removing particulates trapped by plants and mixed with pollen. Unfortunately, the lead also ends up in honey, which Romans ate in abundance and which was a staple for weaning children. Bees and other insects will not live where the atmosphere is too toxic, as Pliny the Elder was aware, and animals were not pastured close to smelters. Even if the most contaminated sites were not used for arable or pastoral farming, substantially increased levels of lead aerosols deposited across a broad region by precipitation will still have affected bees and birds, fish and shellfish in polluted rivers and bays, and cattle and sheep eating grass growing in contaminated soil. Humans who consumed these creatures or their products, including milk and cheese, absorbed lead and stored it in their bones and teeth. Lactating mothers transferred a good deal of this trapped lead, which was released from their bones into their breast milk and hence to their infants.
The lead that permeated the bones and teeth of Romans allows us to distinguish them from those who lived before and after them in the same settlements. Analysis of skeletal remains from Poundbury in Dorset, in southwestern Britain, some distance from the nearest smelting facilities of Somerset, showed greatly elevated bone lead concentrations, more than twice those of pre-Roman skeletons from the same location. At third- to fifth-century cemeteries at Poundbury and at West Tenter Street in London, lead concentrations were in a range from 100 to 250 mg/g, compared with c. 14 mg/g measured in the ribs of thirty-four Neolithic farmers buried in a long barrow at Hazelton, Gloucestershire. Natives of Roman Britain were also far shorter than their Neolithic predecessors and, just as strikingly, shorter than the population that followed them. Women were on average only 152 centimeters (five feet) tall and men 164 centimeters (five feet five inches). The average length of a Roman’s thighbone was between two and three centimeters (about an inch) shorter than that of an Anglo-Saxon. While changes in diet and disease burden after the Roman conquest were consequential, data suggest that Roman-age Britons were on average eating more proteins, including a range of seawater fish and mollusks, than their Iron Age ancestors, which should have led to an increase in stature.
One must wonder, therefore, at the impact of extremely elevated lead concentrations, since any level of lead contamination is known to stunt growth in children.
Excerpted from New Rome: The Empire in the East by Paul Stephenson, published by the Belknap Press of Harvard University Press. Copyright © 2021 by Paul Stephenson. Used by permission. All rights reserved.