Plough

The heavy moldboard plow of medieval northern Europe The light scratch plow suited thin Mediterranean soils but struggled with the dense, wet clays of the north. The heavy plow added a moldboard that turned the sod over and threw it into high ridges, which drained those heavy soils far better. Its breakthrough came around the year 1000, and economic historians estimate it accounts for more than 10 percent of the rise in population density and urbanization during the High Middle Ages. The regions with the most fertile clay gained most, which is a neat measure of how much food had been locked in ground nobody could work.