The invention of the wheel is the ultimate example of human ingenuity due to its elegant simplicity and its vast impact on most modern technology. Here in the context of the element of water, the wheel is a tool for transforming the energy of flowing or falling water into other forms of power. Variations of the water wheel appear in every world culture. While windmills were only suitable at high elevations or on flat plains, flowing streams and the vertical fall of water was ubiquitous. The Romans advanced the technology of the water wheel and its associated mills. While the revolution in industry at the end of the eighteenth century is well known, historians have also described an "industrial revolution of the twelfth century," centered in European monasteries, where a huge variety of clever adaptations of water wheels and associated powertrains automated almost every feature of production. Even our modern hydroelectric facilities conceal within their dams the direct descendant of the water wheel — turbines with curved blades to reduce turbulence, whose rotating shafts turn electric generators.