Mont-Saint-Michel: the tides, the bridge and how to visit

Mont-Saint-Michel is an island about one kilometre off the coast of Normandy, and whether you can walk to it depends on the sea. The tide range in the bay is roughly 14 metres between the highest and lowest water marks, enough to change the view completely within hours.

The short answer to the title: the tides explain both why pilgrims once crossed the sands at their own risk and why France spent more than 200 million euros on a new bridge and a dam. The aim was to push back the silt and make the Mount an island again.

A rock that became an island

According to Wikipedia, the Mount is a tidal island of about 7 hectares at the mouth of the Couesnon River, near Avranches. It rises 92 metres above sea level, and in 2023 it had 23 inhabitants. It is made of leucogranite that solidified about 525 million years ago and outlasted the softer rock around it as erosion reshaped the coast.

Its position is the reason for its history. At low tide it was reachable for the pilgrims who came to the abbey, and the incoming tide made it easy to defend. According to the article, the island remained unconquered during the Hundred Years’ War, and a small garrison fended off a full English attack in 1433. Louis XI later turned it into a prison. Legend says the archangel Michael appeared in 708 to Aubert, bishop of Avranches, and told him to build a church there.

The causeway that caused silt

For centuries the link to the mainland was a tidal causeway, uncovered only at low tide. In 1879 it was replaced by a raised causeway, which stopped the tide from scouring the silt around the Mount. Polderisation of the flats and the canalisation of the Couesnon made it worse, and the bay began to silt up.

In June 2006 the French government and regional authorities announced a 200 million euro project to build a hydraulic dam, using the waters of the Couesnon and the tides to flush out the silt and make Mont-Saint-Michel an island again. Construction started in 2009 and included removing the causeway and its car park.

The bridge and the supertide

Since April 2012 the car park has been on the mainland, 2.5 kilometres from the island. In July 2014 a new light bridge, designed by the architect Dietmar Feichtinger, opened to the public. It cost 209 million euros and lets water flow freely around the Mount, which helps the dam do its job.

Visitors can walk or take a shuttle across it. On 21 March 2015 a supertide, a once-in-18-years event, completely submerged the bridge while crowds gathered to take photos.

The sands are not a shortcut

According to Wikipedia, the Mount can still pose dangers for visitors who avoid the bridge and attempt the hazardous walk across the sands from the neighbouring coast. Medieval pilgrims called it “St. Michael in peril of the sea”, and the name is not just poetry.

A busy island

Mont-Saint-Michel and its bay were inscribed on the UNESCO World Heritage list in 1979. The commune is visited by more than three million people a year and is the most-visited tourist attraction in France outside Paris, so the best hours are early morning and evening.

In practice

• Use the bridge. Walk the 2.5 kilometres from the car park or take the shuttle.
• Check the tide times before you go. The sea changes the view, and a high tide is worth planning around.
• Stay off the sands without a guide. The walk across the bay is hazardous.
• Try the local lamb. According to Wikipedia, agneau de pré-salé, from the salt marshes around the bay, is a regional speciality.
• Go early or late. With over three million visitors a year, the middle of the day is the busiest time to expect.

For other places that manage crowds, see villages that limit tourists and Europe’s tourist taxes.

Frequently asked questions

How big is the tide at Mont-Saint-Michel?

According to Wikipedia, roughly 14 metres between the highest and lowest water marks.

Can you walk to Mont-Saint-Michel?

Yes, across the bridge from the mainland car park, 2.5 kilometres away. Walking across the sands is hazardous.

Why was a new bridge built?

To replace the causeway, which was making the bay silt up, and to let water flow around the Mount again. The new bridge opened in July 2014.

Is Mont-Saint-Michel a World Heritage Site?

Yes, it was inscribed by UNESCO in 1979, together with its bay.

Sources

• Mont-Saint-Michel, Wikipedia: the size, the tides, the causeway and dam project, the 2014 bridge, the 2015 supertide, the history and the visitor numbers.
• Mont-Saint-Michel and its Bay, UNESCO World Heritage Centre: the 1979 inscription. Check the official tourist office for current tide times and shuttle details.