A Renaissance-era letter sealed for centuries barely unfolded and read for the first time

Over 600 years ago, someone folded, sealed and mailed a letter that was never delivered. Now scientists have digitally “unfolded” this and other similarly locked letters found in a 17th century trunk in The Hague, using x-rays.

For centuries before the invention of sealed envelopes, sensitive correspondence was protected from prying eyes by intricate folding techniques called “letterlocking,” which turned a letter into its own secure envelope.

However, the locked letters that survive so far are fragile and can only be physically opened by cutting them into pieces.