Post mills are a type of windmill that date back to the Middle Ages. They are characterized by a rotating structure mounted on a central post, allowing the entire mill to turn to face the wind. This design helps maximize the efficiency of the mill's sails in capturing wind energy to grind grain or perform other tasks. The main components of a post mill include the body, or "buck," which houses the milling machinery, and the sails that catch the wind. Post mills were commonly used in Europe, particularly in countries like the Netherlands and England, before the advent of more advanced windmill designs.