Lead from the Roman era pollutes ice buried deep in an Alpine glacier, providing some of the oldest evidence that mining and smelting during the period spread environmental contaminants across Europe.

A team led by Suzanne Preunkert at the University of Grenoble–Alps in France measured lead and antimony levels in an ice core taken from the Alps’ highest mountain, Mont Blanc, which straddles the French–Italian border. The oldest ice in the core dates to about 5,000 years ago.

Lead levels in the core peak twice in antiquity, once in about the second century bc, when the Romans were expanding their territory, and then again in around ad 120, when the empire was flourishing. Levels of the metal were at least 10 times background levels, suggesting that the mining and smelting of lead spread the contaminant across much of Europe. The Romans used lead for pipes, among other items.

Levels of antimony, an element that is often found in lead ore, increased at about the same time as lead concentrations did — suggesting that early Europeans were breathing in a mix of heavy metals.