Mills
From the stream to the millstone
Before steam, a great deal of turning power came from water. A mill shows a gear train in the open.
Before the Industrial Revolution, power came from three main sources: humans, draft animals, and water. Britannica: gear
In a medieval-style mill, the waterwheel is turned by a stream and is connected to a shaft that leads into the building. Britannica: gear At the other end of the shaft is a gear. Britannica: gear
A series of gears translates the power from the stream to a shaft that drives a millstone, which grinds flour from grain. Britannica: gear
The drawing is our own and not to scale. We have not added named wheels that the caption does not mention.