An unexpected reason for the fall of the Roman Empire: people in Europe experienced a sharp decline in intelligence.

A new study has revealed that at one point during the reign of the Roman Empire, the average IQ level among people across Europe experienced a significant decline. This drop in cognitive abilities was attributed to massive lead emissions produced by the metallurgy industry that supported the empire, according to The Guardian.

The increased mining and processing of iron ores led to a dramatic spike in lead air pollution at the height of the empire. Scientists believe this resulted in a reduction of IQ by 2-3 points throughout the empire.

"We were able to quantitatively assess air pollution over Europe more than 2,000 years ago and evaluate its potential impact on the health of ancient Roman civilization. The results indicated that anthropogenic pollution caused extensive harm to human health for over 2,000 years," said Dr. Joseph McConnell.

Despite the awareness of Roman physicians regarding the dangers of lead, this metal was still widely used for making plumbing pipes, pots, and was also included in medicines, cosmetics, and even children's toys. Additionally, lead was intentionally added to wine after the Romans discovered it helped preserve the wine longer and added a sweet flavor.

While lead poisoning through wine was likely a problem for the upper echelons of Roman society, the rest of the population inhaled it through the air. It is noted that at that time, lead was a byproduct of gold and silver production.

To determine the level of lead air pollution, McConnell and his team studied ice cores drilled in the Arctic. These cores provided a timeline of lead concentration in the atmosphere from 500 B.C. to 600 A.D.

Subsequently, scientists mapped the spread of lead throughout Europe. They then calculated how much neurotoxic metal could have accumulated in children and the potential impact on their IQ.

The data indicated that the average lead level in children at the peak of the Roman Empire could have increased by 2.4 micrograms per deciliter, which would have lowered their IQ by 2.5–3 points. Consequently, the blood lead levels in children could have reached 3.5 micrograms per deciliter.

Some historical records suggest that at the height of its development, the Roman Empire was home to over 80 million people. This implies that about a quarter of the world's population could have been exposed to lead pollution caused by mining and smelting operations. The consequences of such lead poisoning could have been severe enough that scientists do not rule out the possibility that it contributed to the fall of the Roman Empire.

"A decrease in IQ by 2.5–3 points may not seem significant, but such a decline was observed across the entire population of the empire and persisted for nearly 180 years of Roman history," concluded McConnell.

As a reminder, a monstrous volcanic eruption helped give rise to the Roman Empire. The eruption of an ancient volcano in Alaska led to famine and disease, which dismantled the Roman Republic and the Ptolemaic Kingdom of Egypt. In their place, a new state emerged – the Roman Empire.