Sealed letters from the 17th century give away their secrets, without opening them

Computer-generated unfolding animation of sealed letter DB-1538 © the Unlocking History Research Group archive

It has been a few weeks since I wrote to you in order to ask you to have drawn up for me a legalized excerpt of the death of sieur Daniel Le Pers, which took place in The Hague in the month of December 1695, without hearing from you.” At first sight this seems like a normal sentence from a 17th century letter sent from Lille to the Hague. But what makes this sentence so special is that we can read it without opening the sealed letter that contains it.

With new techniques developed by an international research team, it is now possible to read sealed early modern letters. The team’s findings appear in Nature Communications.

X-ray microtomography and algorithms

The team has been able to read a sealed letter that was written over 300 years ago by using X-ray microtomography and algorithms. The X-rays reflected iron particles in the ink—common for inks of the time--, making the words visible. The letter was then virtually opened by a computer-controlled algorithm that pieced thousands of scans together to create legible text. 

Computer-generated unfolding sequence of sealed letter DB-1538 © the Unlocking History Research Group archive
Computer-generated unfolding sequence of sealed letter DB-1538 © the Unlocking History Research Group archive
The fact that they have not been opened and still can give away their secrets is a fine moment for researchers interested in letters, not just for their content but also for their materiality

600 sealed letters in the Brienne collection 

The letter was stored by a post office in The Hague operated by postmasters Simon de Brienne and Marie Germain. In the Brienne Collection of museum Sound and Vision The Hague there are some 600 letters that are still sealed. The fact that they have not been opened and still can give away their secrets is a fine moment for researchers interested in letters, not just for their content but also for their materiality.  

Dr. Rebekah Ahrendt
Dr Rebekah Ahrendt

Why should we (not) open them? 

Rebekah Ahrendt is part of the team and a musicologist at Utrecht University with expertise in paleography and the time period of the Brienne letters(1689-1706). She points out that we only have a tiny portion of letters from this period that are still closed, and the fact that they are closed tells a story. “Why should we open them? The closed letters tell us something about the history of the document as it travelled. These were letters that were unable to be delivered at that time. They were kept safe because they represented monetary value. The recipient would have to pay for the letter. In the case of the Brienne letters the recipient either could not be found or refused to pay the outstanding postage. And so, the postmasters kept the letters hoping someone would pay for them eventually. And indeed, in the postmasters’ records there are entries for when previously undelivered letters were picked up.” 


With these new techniques we can see how a letter was folded and sealed without damaging it, telling us a lot about document security at that time, according to Ahrendt. “Envelopes did not exist, and the senders folded and sealed the letters in a specific way. What does that tell us about how seriously people took privacy? And about people’s interactions with materials? The work of Jana Dambrogio (MIT) and Daniel Starza Smith (King’s College, London) shows that people did adopt different forms of letter folding for different purposes; they call this letterlocking.”  

Daily life at the post office 

Unopened letterpacket DB-1627 was virtually unfolded and read for the first time © the Unlocking History Research Group archive
Unopened letter package DB-1627, Brienne Collection, Sound and Vision The Hague, courtesy of the Unlocking History Research Group archive

There are very few collections like this, providing a glimpse both into the everyday life of average people and into the inner workings of an early modern post office. The closed letter mentioned above was sent from Lille, France by a lawyer called Jacques Sennacques. Ahrendt: "The letter itself is not remarkably interesting. That is not at all surprising because the Brienne letters were from a cross section of society: from hairdressers to noblemen to opera singers. These letters’ ordinariness makes them special, because the correspondence that tends to be preserved is only that of the highest elites.” The letter from Sennacques gives us an idea of  how the post worked at the time. While it does not have a reason for refusal as most letters in the collection do, the fact that this person did not respond to previous letters indicated that he was not in the Hague or that he was dead. It could also be the case that he could not be found.

Merchant in The Hague

The address is very vague. It just says ‘To Monsieur Pierre le Pers, merchant in The Hague’. Even if the address were more specific, they did not have postal codes or house numbers in those days. The closest you could get to an actual street address was something like ‘on the Lange Gracht across from the orphanage’. The postwoman employed by the office, Geertruy Lus, would probably have had to ask around, in places like coffeehouses where merchants spent time together.”  

Postal treaty 

According to the postal treaty between French and the Dutch Republic in effect at this time, all undelivered letters from France should have to been send back. “So actually, this post office in The Hague was violating international treaty law by not sending them back. But sending them back cost money and also eliminated the possibility of making money,” adds Ahrendt. So, Jacques never knew the letter was not read. 

Interdisciplinary work breaks down boundaries 

When Ahrendt first learned about the collection in 2012 (through reading an article from 1938!), it was obvious to her it had much potential. “We really needed a group of people as diverse as possible to examine this collection in any and every conceivable way.” “The project is groundbreaking because scientists from completely different fields collaborated,” explains David van der Linden of Radboud University. “Historians often use letters as a window on people’s past, but they’re also material objects. It is precisely because we collaborated with curators and computer scientists that we began to pay attention to the material features of letters.” 

It is precisely this kind of multidisciplinary, multi-sensory work that will motivate all our fields toward innovation.

A seventeenth-century trunk of letters bequeathed to the Dutch postal museum in The Hague. The trunk belonged to one of the most active postmaster and postmistress of the day, Simon and Marie de Brienne, a couple at the heart of European communication networks © the Unlocking History Research Group archive
The seventeenth-century trunk with the letters, Brienne Collection, Sound and Vision The Hague

Being a musicologist helps 

The letters were hard to read, but being a musicologist helped Ahrendt. There are over 2600 letters and as many different handwritings. “I am a good paleographer. But, my goodness, this was challenging. You do not have an opportunity to compare a person's handwriting. Plus, a lot of these people were barely literate. They wrote in their own dialect and without using any punctuation. They wrote phonetically, with no separation between words, as if they were speaking. The trick that I developed to be able to decipher them is to read them aloud. These letters were also meant to be shared with the whole family or with friends, in the process they were often read to each other." Eleven letters have currently been scanned with XMT (x-ray microtomography). With more funding, the researchers hope to be able to read the remaining sealed letters as well. This will hopefully allow these letters to share their stories with us in the future as well. 


Funded partly by a grant from the Dutch Research Council (NWO), humanities scholars from the Netherlands were able to work together on an interdisciplinary basis with computer scientists from MIT and imaging specialists from Queen Mary University of London. The research team consists of Rebekah Ahrendt (Utrecht University), Nadine Akkerman (Leiden University/De Jonge Akademie), David van der Linden (Radboud University), Jana Dambrogio (MIT Libraries), Amanda Ghassaei (Adobe Research), Daniel Starza Smith (King's College London), Holly Jackson (MIT), Erik Demaine (MIT), Martin Demaine (MIT), Graham Davis (Queen Mary University of London) and David Mills (Queen Mary University of London).

Letterpacket DB-1627 was virtually unfolded and read for the first time since it was written 300 years ago © Courtesy of the Unlocking History Research Group archive
Letter package DB-1627 was virtually unfolded © Courtesy of the Unlocking History Research Group archive