Researchers were able to read the contents of a 300-year-old letter without opening it (Credit: Unlocking History Research Group)

On July 31, 1697, a French lawyer named Jacques Sennacques wrote an urgent message to remind a cousin in the Netherlands to send him a relative's death certificate. To prevent others from reading the confidential memo, the note was carefully folded, or "letter locked." The ancient technique, which transformed the letter into its own secure package, was prevalent before the invention of envelopes.

However, for reasons unknown, the note never reached the recipient and was instead tucked away in a postmaster's trunk, where it remained undetected for centuries. Now, a team of international researchers has deciphered the contents of the over 300-year-old meticulously sealed letter — without opening it!

Written in French and translated into English by the scientists, it said:

Dear sir & cousin,

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. I am writing to you a second time in order to remind you of the pains that I took on your behalf. It is important to me to have this extract you will do me a great pleasure to procure it for me to send me at the same time news of your health of all the family. I also pray that God maintains you in His Sainted graces & covers you with the blessings necessary to your salvation. Nothing more for the time being, except that I pray you to believe that I am completely, sir and cousin, your most humble & very obedient servant,

Jacques Sennacques

Simon de Brienne, a postmaster in The Hague, carefully stored over 3,100 undelivered letters in a trunk (Credit:Museum voor Communicatie, The Hague)

The chain of events leading to this groundbreaking technology began in 2015 when MIT conservator and "letter locking" expert Jana Dambrogio got a call from Daniel Starza Smith, a researcher at King's College London. "He asked me, 'What would you do if I told you there was a trunk with 600 unopened letters?'" Dambrogio told Live Science. "He had me at 'unopened.'"

The treasure trove of sealed correspondence was among the 3,100 letters that had been sitting unnoticed in a trunk at Museum voor Communicatie in The Hague, Netherlands, since 1926. It had once belonged to 17th-century postmaster Simon de Brienne. Historians believe the post office stored the undelivered letters in the hopes of getting paid some day. That's because, in the 17th century, it was the recipient, not the sender, who bore the postage cost. “The idea was that if they kept the letters that weren't delivered, then somebody might eventually turn up for them, at which point they’d get paid,” Rebekah Ahrendt, a music historian and study co-author, told Wired News.

When Brienne died in 1707, he bequeathed the trunk of letters — considered an asset during that period – to an orphanage. Somehow, the chest made its way to the Dutch Ministry of Finance in The Hague and eventually to the postal museum, where it lay until recently.

Since opening the fragile letters would destroy them, Dambrogio and her team decided to develop technology to unseal them virtually. They began by using a high-resolution X-ray dental scanner to create a detailed three-dimensional image of a sealed letter. While the writing inside showed up very clearly, similar to how a tooth shows up on an X-ray, the numerous layers of folded paper pressed close together caused the words to overlap.

Jacques Sennacques' locked letter was among the thousands found in Brienne's trunk (Credit: Unlocking History Research Group)

Amanda Ghassaei of Adobe Research told NPR, "The challenge here was really to try to find a way to manipulate that data and actually virtually unfold it so that we could get it into a flat state and actually kind of generate something that looks like an image of the letter if it had been opened and flattened. But in reality, we haven't even touched the letter."

To solve the issue, the researchers created a sophisticated algorithm capable of deciphering the writing in the cleverly folded letter, crease by crease. The virtual opening allowed the team to read the contents "while preserving letter locking evidence." The algorithm, which was first tested to study a partially-opened letter in 2016, took almost five years to perfect. Holly Jackson, an MIT student who worked on the project, told NPR, "We've kind of been refining this pipeline, trying to make it fully automated, fully generalizable to lots of different intricate folding patterns."

Once perfected, they used it to open four locked letters digitally and fully decode the one from Sennacques.

The researchers used x-ray technology to digitally read the letter (Credit: Unlocking History Research Group)

The scientists, who revealed their revolutionary technology in the journal Nature Communications on March 2, 2021, now plan to decode and translate all the sealed letters in the Brienne collection and exhibit them at the Museum voor Communicatie. Those unable to visit will be able to read the digitized versions on a dedicated website. The new technology will also enable scientists worldwide to study the tens of thousands of unopened historical letters, including the hundreds in the Prize Paper collection taken from enemy ships by Britain between the 17th to the 19th centuries.