In 1926, a seventeenth-century trunk of letters was bequeathed to the Dutch postal museum in The Hague (currently Sound and Vision The Hague), then as now the centre of government, politics, and trade in The Netherlands. The trunk belonged to a postmaster and post mistress, Simon and Marie de Brienne, a couple at the heart of European communication networks. The chest contains an extraordinary archive: 2600 "locked" letters sent from all over Europe to this axis of communication, none of which were ever delivered. In the seventeenth century, the recipient also paid postal and delivery charges. But if the addressee was deceased, absent, or uninterested, no fees could be collected. Postmasters usually destroyed such “dead letters”, but the Briennes preserved them, hoping that someone would retrieve the letters – and pay the postage. Hence the nickname for the trunk: “the piggy bank” (spaarpotje). The trunk freezes a moment in history, allowing us to glimpse the early modern world as it went about its daily business. The letters are uncensored, unedited, and 575 of them even remain unopened. Our international and interdisciplinary team of researchers has undertaken a process of preservation, digitization, transcription, editing, and identification of letterlocking formats and categories that will reveal its secrets for the first time – even those of the unopened letters.