The ﬁrst known windmills were developed in Persia between 500 and 900 AD to pump water and grind grain. They consisted of vertical sails rotating round a central shaft. The ﬁrst documented example of the technology in Europe dates from 1270. It shows a horizontal axis machine mounted on a central post with four sails, known predictably as a ‘postmill’ machine. It took until the nineteenth century for the windmill sails to achieve peak efﬁciency. These sails had some of the crucial features which helped in the design of present-day turbine blades.