In times of political and military unrest, letters were especially vulnerable to interception despite the lengths to which their bearers would go to hide them. Given the often delicate nature of the correspondence, some letters were written in cipher.
This letter, lacking both an address and a seal, was written during the Civil War on behalf of king Charles I, then trapped at Oxford. The writer, George Digby, earl of Bristol, writes to an unidentified party, either Prince Rupert or Prince Maurice, advising that as a result of Oliver Cromwell’s recent incursions, Rupert needs to march on Oxford in order to prevent the city being besieged. Owing to its acute political sensitivity, the letter has been written partially in cipher—or rather a combination of ciphers. Several major players are denoted by numbers: King Charles is 241, Prince Rupert 354, the Marquis of Hertford 223, and so on.