There was a marked difference from the Romans, to what the Franks looked like a few centuries after Rome was gone. The anthikytera mechanism analogy is good, but something big is put into motion by removing Western Rome. It seems we owe a debt to the people who tore down the empire: https://ideas.repec.org/p/pra/mprapa/11027.html : "The water-mill, though known in the Roman Empire from the second century BCE, did not come to enjoy any widespread use until the 4th or 5th centuries CE, and then chiefly in the West, which was then experiencing not only a rapid decline in the supply of slaves, but also widespread depopulation, and thus a severe scarcity of labour. For the West -- those regions that came to form Europe -- the water-mill then became by far the predominant ‘prime mover’: i.e., an apparatus that converts natural energy into mechanical power. " From p. 50 of Change in Byzantine Culture in the Eleventh and Twelfth Centuries: "In the West, water power started to be widely and effectively used in the tenth century for craft production, especially in the wooden industry and for forging; later the windmill was introduced. Byzantium seems to have lagged behind: although water mills were mentioned as early as the seventh or the eight century in the Farmer's Law, millstones turned by donkeys remained the most common means of grinding, and even hand querns continued in use; windmills were unkown until the thirteenth century. There were idiosyncratic experiments..." : https://books.google.no/