A lettre de cachet (French, “signet letter”) in French law was a special form of royal order. In contrast to public lettres de patentes, which were signed by the chancellor and confirmed with the great seal, lettres de cachet were signed by the secretary of state, and sometimes the king, and stamped with the small seal (cachet) of the king (hence also known as lettres de petit signet or de petit cachet). First mentioned in 1560 (Ordonnance d'Orléans, art. 91), they were first used more frequently under Richelieu, peaking at around 23,000 letters between 1741 and 1775 [3. 17].

A lettre de c…