In 1495, Gribshunden, the flagship of King John of Denmark and Norway, burned and sank in the Baltic Sea en route to a political summit in Sweden. Recent archaeological excavation of the shipwreck produced a cemented lump identified using microscale X-ray computed tomography (µCT) as the remains of a purse containing 100+ silver coins. This purse is uniquely informative for several reasons. First, unlike other coin hoards, the date and circumstances of its loss are documented. This reverses the usual situation where coins are used to establish the dating of archaeological features and allow scientists to pose novel questions. Second, this was an unintentional loss, so the coins represent money in circulation and intended for common use, as opposed to hoards, offered as donations or deposited as savings. Third, King John himself was sailing aboard the ship when it sank; these coins were officially sanctioned and therefore offer insights into the king’s monetary policy.