Roman expansion didn't just bring roads and new infrastructure to a conquered Greece but widespread deforestation that fuelled metal production.
Such was the scale of mining for precious commodities it created one of the earliest instances of lead pollution still detectable on the bottom of the ocean today.
The extent of environmental change has been outlined in a new study published in Communications Earth & Environment.
The research draws on core samples from the icy Arctic, peat bogs, lakes and under the Aegean Sea to reconstruct a picture of the region around 2,100 years ago.
Lead author Andreas Koutsodendris from Heidelberg University said the study was part of a broader project to understand how climate impacted early civilisations and the point at which humans started to impact the environment on a large scale.
Metallurgical practices, which involve the extraction and modification of metals, developed on the Balkan Peninsula about 7,000 years ago.
Ores, rocks with desirable minerals inside, containing lead were mined by ancient Greeks and Romans.
When these ores were smelted they released toxic vapour into the atmosphere. This vapour, which contains lead, deposits back into the ground or water, and can be detected in the build-up of sediment layers over time, or as far away as the Arctic in its ice.
Lead pollution was evident more than 5,000 years ago, according to a core sample collected for the study from the Tenaghi Philippon peatland in northern Greece. The bog provides environmental clues from 1.3 million years ago up to AD 300.
"Peat cores don't receive any fluvial [river] input, so it's only atmospheric dust that settles into this environment," Dr Koutsodendris said.
According to the study authors, the results from Tenaghi Philippon represent the oldest instance of continuous lead pollution worldwide.
But the oldest pollution levels in the bog were too low to be detected in 13 marine core samples taken on a series of voyages around the Aegean Sea, located between Greece and Türkiye, for the study.
This suggests low levels of metal production at the time.
But Dr Koutsodendris said the researchers detected a big jump in atmospheric lead pollution levels in the region — from both the sea and the bog — around the fall of Greece in 146 BC as the Roman Empire neared its peak.
These elevated lead levels persisted for about 1,000 years, he said.
[map]Forests decline as mining upticks
During this period, pollen records from lakes around the region indicate a decline in the prevalence of forest trees like oaks.
Dr Koutsodendris said these would have been used to fuel the fires in the smelting process.
The pollen records also show regional increases in olive trees and grass species in line with agricultural expansion.
"In our view, the forests …. didn't really recover to their natural stance," Dr Koutsodendris said.
Larissa Schneider, an environmental scientist at Australian National University, said it was noteworthy that the authors had looked at the marine environment, given research in this field was more often carried out in freshwater and terrestrial settings.
"This highlights the significance of marine archives in documenting environmental changes across broader regions and enhancing our understanding of past pollution events," Dr Schneider, who was not part of the study, said.
"The study also demonstrates the importance of adopting a multidisciplinary approach ... as an effective means of reconstructing past pollution."
Jack Longman, a Northumbria University geographer and environmental scientist who reviewed the study, said the pollution signal from about 2,100 years ago was clear.
"So it looks region-wide, and corresponds to the Roman empire roughly," he said.
Dr Longman said he thought the lack of pollution from the Hellenistic Greek period, pre-Romans rule, was curious.
"[There's] nothing in the records [from] when you would expect the most advanced ancient Greek society, which we would assume was most polluting," he said.
"[It] opens up a load of other questions on this topic."
Tracking the mining boom
While the lands bordering the Aegean Sea were an ancient mining hub, how exactly pollution sources changed over time is unknown.
Dr Koutsodendris said the most recent marine core collecting trip happened as close to ancient mining centres as possible, to try figure out the timeline for different centres of economic activity.
The environmental health impacts on citizens and other organisms at this time are not totally clear either.
There was a level of awareness about some forms of lead being poisonous through the works of Greek poet Nicander of Colophon in second century BC.
And there was a study released earlier this month that suggested lead pollution in the air from 27 BC to AD 180, due to smelting, may have led to cognitive decline in the citizens of the Roman Empire.
Lead pollution around this time may also have had some effect on marine microorganisms, and researchers from the new study are now looking at whether this contributed to historical reports of a decline in fish populations.
"We are doing some studies trying to see if these organisms were affected, to what extent, and what this would mean for food chains in the marine environment," Dr Koutsodendris said.
He added that with lead pollution having a strong impact on ecosystems in Europe in this time period, he wouldn't be surprised if the same thing had happened towards the Levant (where modern countries like Cyprus and Syria sit) and further west.
"The turning point is at 2,150 years before today … from this point onwards [humans] have a really strong [ecosystem] impact on a very wide region," he said.
