Boules de Moulins: The capsules full of 151-year-old letters hidden beneath the Seine

Alysa Salzberg
7 min readMar 18, 2022
(original image source)

The Siege of Paris changed the city in some significant ways. Once-magnificent parks were stripped of their trees or used for pasture, the Comédie Française was transformed into a private hospital, and the southern reaches of the city suffered damage from roughly a month of shelling from the Prussians. And yet, there are no traces of any of this today.

The physical remains of the Siege of Paris are instead small-scale items, like the bread souvenirs I wrote about a few months ago. Or the metal cylinders full of letters that are still buried beneath the Seine.

During the Siege, Parisians weren’t able to get or receive mail or telegrams the usual way, making them truly cut off from the world. The silver lining to this was that it led to some innovative solutions.

Ask any fan of aeronautical or philatelic history and they’ll tell you that the concept of regular airmail was developed during the Siege, when balloons bearing letters were regularly sent into the skies. Most of them were actually able to deliver letters from besieged Parisians (I’ll write about this in a future article). But on the other hand, there was no consistent way for Parisians to receive mail from beyond the city walls.

Homing pigeons were used, many carrying letters on cylinders of microfilm. René Dagron, who had patented microfilm in 1859, had proposed his services to the French government during the Siege, and this ultimately allowed for 115,000 messages and newspapers to be sent to Parisians.

While that’s an impressive amount of correspondance, far more pigeons and the messages they carried never made it back to the capital, whether because they got lost, flew into bad weather, or were shot down by the Prussians.

But three inventors, Pierre-Charles Delort, Émile Robert andJ. Vonoven, came up with what might have been a brilliant plan: boules de Moulins (balls from Moulins, the city where they were manufactured and sealed). These hermetic zinc containers (which were actually more cylindrical than ball -shaped) measured 20 cm (7.87 inches) long and 12 cm (4.72 inches) in diameter and could contain up to 600 letters.

A boule de Moulins that’s been opened. (Image courtesy of le Musée de La Poste and Google Arts & Culture)

The letters could be sent from anywhere, even countries outside France. They just had to be marked “Paris par Moulins” (“Paris via Moulins”). Once they arrived at Moulins, they were collected and rolled into one of the boules, which was then welded shut. The cost of sending a letter this way was (understandably) high.

The sealed boules de Moulins were taken by carriage to the farthest unoccupied areas of the Seine and then dropped into the water.

Boules de Moulins were intended to lay low, since they’d easily be spotted by the Prussians if they floated on the surface. Instead, they were meant to roll along the river bottom, rotating and moving with the current thanks to their raised metal ridges, until they eventually reached a net that had been spread to catch them just outside Paris.

You can see what a boule de Moulins looked like, how it was sealed, and how it was supposed to move in the water, at the 1:40 mark of this video.

The plan was ambitious, but it might have worked. After all, pigeons were delivering microfilm. It was the 19th century, an era of invention, curiosity, and industry — anything was possible! And to be fair, a few boules de Moulins had been successfully tested in the Bièvre, a river that ran up Paris’s Left Bank (it was covered over in 1912).

Unfortunately, things didn’t exactly go to plan. Or, as several French sources like to say it was un échec total (a total failure).

For one thing, by the time the boules and the method for sending them had been set up, the Siege was already in its last month. Still, a lot of people wanted to send messages to loved ones, friends, and business associates in Paris! Between January 4 and the armistice on January 28, fifty-five boules de Moulins were released into the Seine.

But of those…not a single one reached Paris before the end of the Siege.

A few boules de Moulins were retrieved in various areas along the Seine in February and March 1871, when the Siege was over. The rest, it seemed, were gone. Many sources speculate that the net near Paris was damaged by ice — an unusual factor that the boules’ inventors didn’t seem to consider, since the Seine rarely freezes. Unfortunately, the winter of 1870–1871 was exceptionally harsh and cold.

So, if they didn’t reach Paris, what happened to all those other boules de Moulins?

Some may have floated all the way out to the Atlantic Ocean, lost forever. But according to the Musée de la Poste, about thirty of the fifty-five boules have been found. In addition to ones found shortly after the Siege, individual boules de Moulins were retrieved at various spots along the Seine in 1942, 1952, 1968, 1982, and as recently as 1988.

Many sources also postulate that other boules de Moulins may have been found but those who discovered them haven’t come forward, either because they didn’t know what they’d found, or because they wanted to keep the boule and its contents for themselves.

One of the reasons for the latter is that letters with the special address and postage from a boule de Moulins are worth a lot in the philately community. For instance, this 2020 article in Le Monde mentions a boule de Moulins letter that was found in March 1871 and was up for auction for an estimated price of 12,000 euros.

The letter, which was labeled “found in a container washed up on the banks of the Seine, at Quillebeuf (Eure department), March 26, 1871” after it was found. (image source)

Letters from boules de Moulins are not only rare because so few of the boules have been recovered; the letters that have been found were still delivered to the person they’re addressed to (or to their descendants, if it was possible to locate them), because the French Postal Service still considers them their responsibility. Respect.

Today, you can see a boule de Moulins at the Musée de La Poste (Postal Museum) in Paris. Some others have been auctioned off and are now in private collections or in other museums.

I hope the latter is more common than the former, but it’s hard to find a lot of museums showing a boule de Moulins in their online collections.

You may also spot a boule de Moulins on an old postage stamp; in 1979, the French postal service issued a stamp celebrating this ambitious but failed mail delivery system.

(image source)

More recently, a luxury jewelry brand started making boules de Moulins pendants. Unfortunately, while I was waiting for a special occasion to come around so I could suggest it as the perfect splurgy gift for yours truly, the line was discontinued.

On the other hand, I got to see a real-life boule de Moulins for the first time at the amazing France-Allemande(s) exhibit at the Musée de l’Armée in 2017. It was an unexpected and astonishing sight. At the time, I didn’t realize that the letters curled tightly inside were copies, since the originals had all been delivered!

A photo I took at the exhibit.

Just as exciting is the idea that there are still other boules de Moulins out there, buried in the Seine. Will any more of them turn up one day?


A Beauty and the Beast retelling set during the 1870–1871 Siege of Paris, Hearts at Dawn has been selected as a Historical Novel Society Editors’ Choice book. It’s currently available in Kindle and paperback formats and is part of the Kindle Unlimited Library. I hope you’ll give it a read!

And if you do, I’d be forever grateful if you left an honest review on Amazon and any other sites or social media platforms where you post. Reviews help books gain more visibility and credibility. Even a review of a short few lines can be incredibly helpful.

I hope you enjoyed this dive into boules de Moulins. Feel free to subscribe to this blog or follow me on Goodreads or Amazon to find out when I publish new posts.

Until next time!



Alysa Salzberg

is a writer & worrier. She recently published her first novel, “Hearts at Dawn”, a Beauty & the Beast retelling set during the 1870 Siege of Paris.