Waterwheels & Windmills
Simple, horizontal waterwheels were used by the 2nd century bce in both China and Europe. Roman engineer Vitruvius (31 bce–14) described them. No one knows who invented waterwheels.
There were occasional instances where waterwheels were used to grind grain during imperial Roman times, but Emperor Vespasian (69–79) reputedly rejected using a water-driven hoist to raise boulders for fear of engendering unemployment.
Whether slave or free, labor was cheap in the Roman empire. No need was seen for labor-saving devices. That would change, even in Roman times: in the 4th century, an immense flour mill at Barbegal in southern France employed 16 overshot watermills.
A survey of England in 1086 counted 5,624 waterwheels in 3,000 villages. Most of the waterwheels were vertical, overshot wheels with complicated gearing. England at the time was by no means the most advanced country in Europe, either economically or technologically.
By the beginning of the 14th century waterpower was used for grinding, crushing, and mixing many materials, in the making of paper and cloth, among other things, as well as moving bellows and trip hammers for furnaces and forges.
As early as the mid-11th century a waterwheel powered by the movement of the tides was used in Venice. Within the next few centuries many other such wheels were erected on the seacoasts of Europe.
Despite their utility waterwheels had limitations, starting with the need for flowing water. This made them unsuitable for dry or marsh lands.
Windmills appeared on the plains of northern Europe in the 12th century. They were especially important in the Low Countries (which were mostly marsh).