WORLD

Modern people aren’t the only ones who’ve polluted the atmosphere. Ancient air pollution has now allowed scientists a peek into the economic health of Ancient Rome. (Science)

Use our rich collection of resources to learn more about the geographic, cultural, and political atmosphere of Ancient Rome—and decide for yourself if it was polluted.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• Scientists are now able to track the industrial health of Ancient Rome by measuring the amount of lead pollution in air and soil. How does air pollution correlate to Ancient Rome’s economy?
  • This type of pollution is associated with the production of silver, which was used to make Rome’s standard unit of currency, the denarius.
    • As Rome prospered or expanded, more denarii were minted and circulated throughout the territory. This required more silver to be mined. These periods of economic growth generally correspond to periods of greater lead-based air pollution.
    • As the Roman economy slowed due to wars, civil unrest, or disease, fewer denarii were needed for circulation. These economic downturns are associated with reduced coin production and lower levels of lead-based air pollution.
    • “It’s really the rise and fall of a monetary system based on silver,” says one historian.

• OK, but what does mining silver from the earth have to do with lead in the air?
  • A lot. Silver rarely exists as pure, elemental ore. Instead, it is more abundant in minerals, usually mixed with other metals such as copper, zinc, and lead. To obtain silver, Roman metalsmiths smelted silver in a two-step process.
    • First, minerals were heated until the metal separated from the rocks.
    • Second, the silver-lead alloy was heated to at least 960° Celsius (1,760° Fahrenheit)—the melting point of silver. At this temperature, the lead burns to lead monoxide, some of which escapes into the atmosphere. The new research suggests this lead pollution drifted with air currents over the Atlantic before falling as precipitation on the still-growing Greenland ice sheet.
      • Liquid silver was then poured into rectangular molds. When these silver bars (ingots) cooled, they could be easily transported across the empire for minting as coins or luxury items.
      • Lead was not merely a waste product in Ancient Rome! It was the metal used for plumbing the empire.
      • Ancient Rome’s most productive silver mines were in provinces of Hispania and Baetica (Spain and Portugal), Gallia Aquitania (France), Britannia (Great Britain), and Achaea (southeastern Greece). Scientists associate the Greenlandic lead with mines in Hispania and Gaul. Here’s a great map of Roman provinces around 125.

• How did scientists measure 3,000-year-old air pollution?
  • ice cores. Scientists “measured lead levels along a roughly 400-meter cross-section of Greenland ice, representing layers that froze between 1100 BCE and 800 CE. They melted the ice bit by bit, from one end to the other, and siphoned off the ice melt for analysis—obtaining around 12 measurements per year during the Roman era.”

• The lead levels in the Greenlandic ice rose and fell as Rome underwent economic change. What factors might contribute to a slower economy and lower levels of air pollution?
  • wars. Lead levels dropped dramatically in the years Rome fought with Carthage in the Second Punic War (218-201 BCE). More government funding was directed at military expenditures (such as weapons and ships) than minting coins.
  • politics. The transition from the Roman Republic to the Roman Empire was a period of civil conflict (including a memorable exchange in the Senate) and economic stagnation as Romans were wary of investing. Fewer denarii were circulated and lead levels were low in the last years of the republic.
  • disease. The Antonine Plague was a pandemic (probably smallpox) that devastated the Roman Empire between 165 and 180. As many as five million Romans died, with the military and merchants being particularly hard-hit. Infrastructure crumbled, trade was slowed, and lead levels fell.
  • debasement. Debasement is the process of devaluing currency. Denarii underwent a slow process of debasement (reduction in silver) in the centuries following the establishment of the empire. As the Roman government reduced the amount of silver in its coins, lead levels consistently fell.

• Lead pollution was highest during the height of the Roman Empire, which Science identifies as the first century CE. What factors might have contributed to a wide circulation of coins (and air pollution) during this time period?
  • Pax Romana. The Pax Romana was a long period of peace and stability associated with Rome’s first emperor, Augustus. (That’s him on the denarius up top.) During the Pax Romana, the Roman Empire enjoyed a relatively stable political system, reliable administration and infrastructure, and secure borders. The Roman Empire expanded to its largest size and supported its largest population during the Pax Romana.
    • The circumstances of the Pax Romana meant there were more people able to spend more denarii on a large scale. (They didn’t have to spend it fighting wars and disease.) The Roman government could also spend money on infrastructure such as government employees and contractors—who were paid in denarii.
    • Research suggests that Western Europe may have seen higher lead emissions during the Pax Romana than at any time prior to the Industrial Revolution. (!)

TEACHERS TOOLKIT

Science: Rise and fall of Roman Empire exposed in Greenland ice samples

Nat Geo: Ancient Rome

(extra credit!) Proceedings of the National Academy of Sciences of the United States of America: Lead pollution recorded in Greenland ice indicates European emissions tracked plagues, wars, and imperial expansion during antiquity