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Wind power [was never] taken seriously in the ancient world [...] though Hero of Alexandria described a windmill connected to an air pump designed to blow an organ, there is no evidence for the existence of any rotary windmills before the tenth century CE.

- Ancient Technology, pg 17.

Mechanical knowledge had a long way to go in antiquity, but my understanding is that the Romans and Hellenistic Greeks made limited but significant use of water power for mills, clocks, and more rarely, automatons. My question here is pretty straightforward: Are there any clear reasons why wind power was never used, especially considering that watermills require a constant and fairly heavy flow of moving water? (Not that you can set up a windmill just anywhere, but it's surprising to me they don't appear as an alternative in areas without strong rivers.)

For this question please take antiquity to mean the Mediterranean and Near Eastern world from the end of the Bronze Age in 1200 BC up to the decline of Rome around 500 AD.

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    Engineering wind is harder - it changes far more widely and quickly than water. – Jon Custer Dec 21 '18 at 4:05
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    Who needs windmills when you've got plenty of slaves? And later on, serfs. – jamesqf Dec 21 '18 at 5:19
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    @jamesqf you do not need to feed the wind. – SJuan76 Dec 21 '18 at 8:01
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    Interesting question but probably difficult to answer. @JonCuster 's comment is probably at least part of the answer. – Lars Bosteen Dec 21 '18 at 8:14
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    @Jon Custer: Wind is super hard. Wind changes direction unpredictably, and varies greatly in strength. Even modern wind turbine has to be locked down when the wind is too strong. – sofa general Dec 21 '18 at 16:28
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I believe windmills have to wait until the late Middle Ages because, due to the inequities of the cube-square law, making life size operational windmills is very difficult.

The cube-square-law is a consequence of the areal surface rising as the square of the dimension while mass increases as the cube. However the strength of a material is proportional to the areal surfaace, and in a windmill so is the motive power collectible from the wind. However the loads are increasing much faster as one scales a model up to real life.

However the wind itself, due to air's low density, is a much weaker motive force than is for example water. Further, even with modern materials it is not possible to construct windmills that can operate safely in high winds - so it is necessary to rely only on moderate breezes. A further requirement on the materials is that to catch the wind the wheel must usually be elevated, far from the mill itself at ground level to be convenient for loading an unloading. This in turn requires higher performing materials, such as high grade steel.

In order to overcome friction the tolerances on the horizontal-vertical-gear must be very precise. It was only with the perfection of casting techniques developed for first bell making, and then cannon manufacture, that the necessary tolerances were achieved for high strength steel products. This occurs in and around 1200, just when the first vertical plane windmills appear in Europe.

it is true that horizontal-plane windmills are attested in the Middle East and China from several hundred years earlier, but these were inefficient due to the necessity of shielding half the turbine from the wind.

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  • An interesting and technically precise answer, thanks! – Era Dec 22 '18 at 16:12
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    Another factor is that water mills can be constructed to deliver reliable and constant power (barring serious droughts, of course). Build a dam and mill pond, and as long as the inflow from the stream is more than the amount of water used to power the mill, it will deliver reliable power whenever you want it. Wind, OTOH, is only available when and how the wind blows. Something that's still true today, if you compare wind farms to hydroelectric plants. – jamesqf Dec 24 '18 at 5:32
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Jos explained correctly that windmills were not used in antiquity (and in the modern epoch they appeared after water mills). The main use of wind power in antiquity was for sailing. Sails were the principal propellant for long distance water travel since the time immemorial. Rowing can be used only for short distance and in battle. All sea trade was made using sailing vessels.

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Hero of Alexandria also invented a working steam engine, but we had to wait for James Watt for common use of it. When something becomes technically possible, that doesn't automatically say it will be implemented. We'd be using thorium reactors otherwise.

First of all, there was a serious labor conflict. Roman and Greek societies were slave based. Nobody was waiting for unemployed slaves, to say the least.

Second, it was expensive technology. The people with the wherewithal to finance water and windmills had already invested that money. In slaves. There was no reason for them to finance in expensive and possibly tricky technology, with the added risk of unhappy slaves and more importantly a very unhappy electorate.

In those days that technology was complicated, difficult to operate, very maintenance sensitive and outright dangerous (both to operators and bystanders*). You needed skilled staff to operate and maintain it. Those guys were relatively expensive, both in training and salaries.

*= I did see some documentaries in which medieval replica wheeled cranes are used. Kind of giant hamster wheel with ropes and pulleys to lift heavy objects. Those cranes were really dangerous. They could very easily be overloaded and break, with devastating consequences.

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    I am not sure if a clever Greek scientist imagining a possible wind-powered device in the Antiquity would understand at once its eventual consequence on the labour market or on slave sociology, nor that it would necessarily stop him... – Evargalo Dec 21 '18 at 13:02
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    @Evargalo He could design what he wanted. That wasn't an issue. After designing it he had to market it. And that's where de drachme stopped. – Jos Dec 22 '18 at 7:36

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