The heavy plough and the agricultural revolution in medieval Europe

This research tests the long-standing hypothesis, put forth by Lynn White, Jr. (1962), that the adoption of the heavy plough in northern Europe led to increased population density and urbanization. White argued that it was impossible to take proper advantage of the fertile clay soils of northern Europe before the invention and widespread adoption of the heavy plough. We implement the test in a difference-in-difference set-up by exploiting regional variation in the presence of fertile clay soils. Consistent with the hypothesis, we find that regions with relatively more fertile clay soil experienced increased urbanization and population after the plough had its breakthrough, which was approximately around the closing of the first millennium AD. We find that the heavy plough accounts for more than 10% of the increase in population density and urbanization during the high middle ages.