The Roman Empire’s achievements in infrastructure, sanitation, public health, and governance are widely celebrated. However, alongside these advancements, a recent study highlights a darker legacy: widespread lead pollution that caused an estimated 2- to 3-point drop in IQ across Europe during the Pax Romana.
The findings, published in the Proceedings of the National Academy of Sciences, suggest that the vast expansion of mining and metal processing during the Roman Empire significantly increased airborne lead pollution, affecting the health and cognitive development of populations across the continent.
The Scale of Roman Lead Pollution
Researchers traced the origins of this pollution to the empire’s booming metal industry, particularly its massive mining and smelting operations. Lead, a byproduct of refining silver and gold, was not only a pollutant but a widely used material in Roman daily life. It appeared in water pipes, cookware, cosmetics, toys, and even in wine preservation, as Romans discovered lead-based syrups could sweeten and extend the shelf life of their beverages.
Dr. Joseph McConnell of the Desert Research Institute in Nevada, the study's lead author, described the findings as profound. "It’s amazing that we could quantify air pollution levels from nearly 2,000 years ago and assess their health impacts on ancient Roman civilization," he said. "This study shows that industrial activities have been damaging human health for over two millennia."
Quantifying the Impact
The researchers analyzed ice cores drilled from the Arctic to measure historical lead concentrations in the atmosphere. The data revealed a dramatic increase in lead pollution around 15 BC, coinciding with the rise of the Roman Empire. These elevated levels persisted for nearly 180 years, peaking during the Pax Romana—a period of relative peace and prosperity that ended in AD 180. Over this time, the empire released an estimated half a million tonnes of lead into the atmosphere.
Using atmospheric models, the researchers mapped how lead particles spread across Europe. Modern studies on lead toxicity provided further insights into how these pollution levels likely affected human health. At its peak, lead exposure in children could have caused blood lead levels to rise by approximately 2.4 micrograms per deciliter, resulting in an average IQ reduction of 2.5 to 3 points. Accounting for background exposure, children’s blood lead levels may have reached 3.5 micrograms per deciliter—levels known to impair cognitive function.
A Population-Wide Decline in Cognitive Ability
With the Roman Empire’s population estimated at 80 million during its height, nearly a quarter of the world’s people may have been exposed to harmful lead pollution. The cognitive effects, while seemingly small on an individual level, would have compounded across an entire population over nearly two centuries.
"A 2.5- to 3-point reduction in IQ across the population is significant, especially when sustained for 180 years," McConnell noted. "Whether these health impacts influenced the course of history is a question for historians and archaeologists."
Lead’s Lingering Legacy
Lead pollution didn’t disappear with the fall of Rome. While airborne lead levels decreased during the early medieval period, they surged again in the High Middle Ages and peaked during the 20th century with industrialization and the widespread use of leaded fuels.
Modern regulations have mitigated the effects of lead pollution. For instance, a 2021 study by the Centers for Disease Control and Prevention (CDC) found that blood lead levels in U.S. children dropped dramatically from 15.2 micrograms per deciliter in the late 1970s to 0.83 micrograms per deciliter by 2016, following the banning of leaded fuels.
A Health Warning Echoing Through History
The Roman experience serves as a cautionary tale of how industrial progress can harm public health. Despite their awareness of lead’s dangers—some Roman physicians recognized its toxic effects—the empire continued to rely heavily on the metal.
As McConnell and his team demonstrate, the consequences of this reliance were far-reaching, affecting not just the Roman population but leaving a toxic legacy that persisted for centuries. Today, the study serves as a reminder of the importance of balancing technological advancements with environmental and public health considerations.
