Letters close (Latin: litterae clausae) are a type of obsolete legal document once used by the Pope, the French and British monarchy and by certain officers of government, which is a sealed letter granting a right, monopoly, title, or status to an individual or to some entity such as a corporation. These letters were personal in nature, and were delivered folded and sealed, so that only the recipient could read their contents.[1] This type of letter contrasts with the better-known letters patent.
It was necessary to break the seal to open and read the letter, and so its arrival with the seal intact showed that it had not been intercepted or tampered with. However, once the seal was broken, it could no longer confirm the authenticity of the document.