Waterwheels. The Romans used waterwheels for various industrial applications, but they were not exploited to their fullest potential until the Middle Ages, when new configurations of the watermill allowed them to do heavy work even when powered by modest streams. A watermill was often the centerpiece of any village in western Europe—and in the European settlements of North America, where, after the church, the first structures built were mills to produce things such as flour, lumber, iron, and mash (for brewing).

Available Water Sources. Waterwheels were especially prevalent in western Europe during the Middle Ages. The reason was geographical. Because that part of Europe receives more rainfall than the Mediterranean basin, it has more rivers and streams that flow swiftly and year round. Mills could be located in more areas than were possible in the Roman Empire, and...