Lead pollution in Arctic ice shows economic impact of wars and plagues for past 1,500 years 

A research team used 13 ice cores from Greenland and the Russian Arctic to measure, date, and analyze lead emissions captured in ice from 500 to 2010 CE. They found that increases in lead concentration in the ice cores track closely with periods of expansion in Europe, the advent of new technologies, and economic prosperity. Decreases in lead, on the other hand, paralleled climate disruptions, wars, plagues, and famines.

Source: Lead pollution in Arctic ice shows economic impact of wars and plagues for past 1,500 years — ScienceDaily