When most of us think of a windmill, we think of the quaint Dutch variety, which are so emblematic of Holland that the 19-windmill complex in the village of Kinderdijk has been named a UNESCO World Heritage Site. Those towering windmills with their lattice-shaped blades, widespread since before the days of Don Quixote (finished in 1615), weren’t keeping the lights on, like today’s wind farms. So what did they do?

In the windy Netherlands, those quaint structures were an important part of flood control beginning in the 15th century. A quarter of the country lies below sea level, which makes it incredibly prone to flooding. The Dutch have refined their flood control systems over hundreds of years, and their engineering is so effective that other countries, like the U.S., are now trying to adopt their techniques as climate change puts more cities at risk of flooding.

Windmills harnessed the power of wind to pump water out of what are called polders, swampy areas reclaimed from the water and turned into arable farmland. Windmills pumped the water out of the low-lying ground to prevent flooding and keep crops from drowning [PDF]. They could draw water up almost five feet, where it would be stored before being drained into rivers or back into the sea. If water needed to be raised more than five feet, mills were installed in a series, called a molengang, so that the first mill would lift the water five feet, then a second higher mill would lift another five feet, and so on until it could drain into a canal.

According to a translated 1962 history of Dutch windmills by windmill preservationist Frederick Stokhuyzen, there were about 9000 windmills in Holland in the 1800s, and the earliest mentions of Dutch windmills date back to the 13th century. Before polders were established, windmills—as the word itself might lead you to believe—were already places to grind grain and mustard seeds. Wind power was also used to cut timber, make paper, and press oil—essentially, anything that needed to be pounded, shredded, or mixed. Aesthetically, these windmills looked much the same from the outside, though their interior machinery and layout were different.

The interior of a tower mill. Image Credit: Frederick Stokhuyzen via University of Groningen

In larger windmills, including drainage mills, the miller tended to live on the lower floors of his workplace, much like a lighthouse keeper would.

Author Peter Moore discusses the life of a miller in his history of weather forecasting, The Weather Experiment: The Pioneers Who Sought to See the Future, noting that working at a wind-powered mill required serious skill.

“The art of windmilling is almost completely lost today but in [the 1800s] it was a common practice that required mental alertness,” Moore wrote. The miller “would have worked inside, operating the gearing system, rotating the sails and applying the brake when the wind blew too strongly. This was a real danger.”

He continued:

"If the sails were not furled in a storm its arms could spin around at an ever-quickening pace, propelled by its own force as well as by that of the wind. The friction of the movement had been known to set mills alight, as had attempts to belatedly jam the brake wheel. The miller, therefore, had to be attuned to coming weather, judging the subtle shifts in the cloud base, the dimming of the ambient light or the quickening of the breeze."

“Harbor with Windmill” by Jan van Vlaardingen Couver via Wikimedia Commons // Public Domain

Dutch windmills also served as messengers. Millers broadcast news—including whether the mill was open for business—by adjusting the position of the windmill’s sails. Tilting the sails to look like a lopsided “X” could indicate joy or mourning, depending on where the sails were located in relation to the vertical. If the top sail was a little before the vertical, that indicated joy (for births, weddings, etc.); if it was just past the vertical, that meant mourning (for funeral processions). During World War II, resistance forces used windmill blades to spread information about Nazi raids.

Windmills were so integral to life in the Netherlands that they are ubiquitous in Dutch landscape paintings. Certainly they’re more picturesque than the American mills that powered textile production and other industries in the 19th century, though they may not have had the same mass production abilities.

However, windmills no longer play the vital role in industrial production in the Netherlands, nor are they the most effective form of flood control anymore. There are only about 1200 left, many of them in the western region of Holland, though the whole country still celebrates them on the second Saturday and Sunday of May for National Mill Day.

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