Atmospheric lead pollution is not a recent phenomenon, not even a product of the industrial age, which began in the late 18th Century. Swedish researchers analysing lake sediments found that an increase in lead levels began more than 2,600 years ago, peaking some 2,000 years ago. This coincided with an expanded use of lead during the Greek and Roman Empires. Another increase began about 1,000 years ago, accelerating during the 19th and 20th centuries. Researchers point out that pre-industrial cumulation (from about 600 BC to AD 1800) was at least as large as the cumulative deposition during the industrial age.