In their study, the researchers examined soil cores from Ostia, Rome’s earliest harbor, where the city’s water runoff drained. Layers of lead in the soil “corresponded to periods in the Roman Empire when there was a lot of economic growth,” Newitz says. “And so the more lead they saw, the more pipes they speculated were in use during that period of time, and they saw a lot of really interesting patterns.”
“Basically, as the pipe system expanded, what it meant was that the Empire was spreading,” she says, explaining that Romans sourced their lead from European colonies, making the city’s water infrastructure hugely expensive to build and maintain.