How a new dam saved the island of Mont-Saint-Michel

Mont-Saint-Michel recently celebrated its 1,000th birthday. The stunning abbey is famed for its isolated location, sitting roughly a mile off the shore of the French mainland. Over time, however, the bay was silting up, leaving the commune surrounded by sea on only a few rare occasions in the spring. 

That was until a new dam was built saving Mont-Saint-Michel’s status as a tidal island.

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(Getty Images)

Over the years, Mont-Saint-Michel has served a variety of different purposes. From its outset, the monastery in Normandy was a holy sight for of pilgrims, accessible to them depending on the tides. A Romanesque abbey was constructed in the 11th century, designed by the Italian architect William of Volpiano upon the request of Richard II, Duke of Normandy. 

It also served as a sight of military importance, its unique location making it easier to defend. English forces besieged the commune twice during the Hundred Years’ War, but in both 1423 and 1433 their efforts were in vain. Mont-Saint-Michel remained unconquered throughout the protracted war. 

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During high tides, Mont Saint-Michel was still largely surrounded by sand. (Getty Images)

Louis XI became King of France in 1463, soon after the war ended. He saw the unique strategic advantages of Mont-Saint-Michel and began using the island as a prison. It served in this function for centuries, regularly used as a prison for the French monarchy throughout their rule, right up until Louis XVI was deposed in the French Revolution. Over these years, the abbey’s status as a holy site had waned. Fewer pilgrims visited and by the time revolution gripped France in 1789, very few monks still lived on the island. 

More recently, it has been one of France’s most popular tourist attractions. The abbey has developed into the breathtaking building it is now, the spire placed at the rock’s highest point, and it has been a UNESCO World Heritage site since 1979. Over 2.5 million tourists visited the island in 2022 alone.

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Cloisters at Mont Saint-Michel. (Getty Images)

Throughout this storied history, Mont-Saint-Michel’s status as an island was central to its purpose. For all of its architectural and spiritual value, the geography of the tidal island was at the center of its appeal. 

This is why a dam 20 years in the making was constructed. It is now hailed as having saved the island, reversing the silting of its bay. This had been caused by an old dam, built across the  Couesnon River. While this protected the town of Pontorson from flooding, it had prevented the river’s outflow during low tide. For centuries, the outflow had cleared sediment from the bay at Mont-Saint-Michel, ensuring that it remained an island at high tide. 

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Celebrating the 1,000th anniversary of the abbey this summer, French President Emmanuel Macron said: “In order to transmit, one must preserve, but for decades Mont-Saint-Michel threatened to silt up completely, which would have realized the old dream of English generals, to take the mount as if it was a hilltop amid fields.

“In just a few years, the silting up of the bay has been stopped and we have restored the possibility of an island,” Macron continued.

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A view of Mont Saint-Michel from the Couesnon River. (Getty Images)

Work on the new hydraulic dam began in 1995 and was completed in 2015. 

Though the aim is to restore Mont-Saint-Michel to a full tidal island, it is now accessible year-round. A visitor parking lot has been moved onto the mainland, and from here tourists can visitors reach the abbey via shuttle buses, foot or bicycle, crossing a bridge built in 2014. It stands on stilts that allow water to pass underneath.

Check out our original video on Mont-Saint-Michel below:

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