Great Structures - Tower mills: Rotating caps that powered European industry

Constructed from brick or stone masonry, the tower mill introduced a breakthrough to vertical windmill design with a movable wooden cap that could turn its sails directly into the wind. Because its sturdy base allowed it to reach higher elevations than earlier post mills, it captured more wind with larger sails. For nearly six hundred years between 1300 and 1900, tower mills generated twenty-five percent of Europe's wind-driven industrial power, proving essential before the dominance of coal and steam engines.

Source: Wikipedia