A mill powered by the wind, used to grind material. There are several types - the post type first appears in the Medieval period, smock and tower are generally later. These rely upon a slight wind to turn sails, which turn internal machinery to turn millstones. In the event of high wind speeds damage may be caused to the machinery - so there are mechanisms to reduce the sail area in proportion to the wind-speed. Windmills are situated on the tops of hills or near the coast in Northumberland and Durham - where the earliest record is one on Coquet Island in 1248AD. They were widespread use till steam-driven mills - though the interest in windmills as part of the picturesque meant that one was built in the 1920s near Ponteland, though was never intended to be used as such.