First windmills

It is not known exactly where or when the first windmills were constructed, but it likely happened in Sistan (an arid region that today spans the border between Iran and Afghanistan) during the 9th or 10th century CE. The type of mill was what's called an "Asbad", a vertical shaft mill built within walls that direct the wind through the sails (these are also sometimes called panemone windmills).

The earliest known description of a windmill comes from the writings of al-Masudi, a geographer and historian from Baghdad. In 943 CE he wrote: "Sistan is called the land of wind and sand, where the wind spins the mills, takes water out of the wells and waters the gardens." A similar reference was made to the region's windmills by the geographer Ibn Hawqal who travelled the region between 943 and 969 CE. In his chronicle Surat al-Ard he states, "in Sistan the severe winds are blowing constantly, and thus people have built wind-mills for grinding grain into flour".

The first writer to describe the mills of Sistan in any technical detail was Ansari-yi Damishqi, whose early 14th century geography of the region included a simple sketch of a Sistani mill. From this we can be fairly sure that the ancient mills of Sistan were built to broadly the same design as surviving 18th century asbads on the Plain of Khaf in eastern Iran.

An asbad consists of a low, bunker like building with a set of tall freestanding walls on the roof. These walls form a three-sided enclosure that is fully open on the side facing away from the prevailing winds, and has a narrow, doorway-like aperture in the windward side. Inside this enclosure is a vertical wooden shaft with sails radiating out from the centre, but oriented parallel to the shaft. When the wind blows through the aperture, it pushes the sails and rotates the shaft, while the sails on the returning side are protected from the wind by the walls. The shaft is directly connected to a millstone inside the lower building. Many also have a grain-feed mechanism that is linked to rotation of the shaft, allowing it to be left running without human assistance.

The earliest references to windmills in Europe date from the 1100s. It is likely these were developed independently, though it is possible that they were inspired, at least in concept, by descriptions given by travellers who had visited the east. The oldest unambiguous reference to a windmill in Europe comes from the village of Weedley, Yorkshire, in 1185.