Autograph letter to his mother-in-law, the president of Montreuil. (Dungeon of Vincennes, June 1, 1778); 1 page ½ in-4°. Beautiful letter before his transfer to the royal prison of Aix-en-Provence. The Marquis de Sade, tested, relies entirely on his mother-in-law who is in charge, for the smooth running of his trial and for his honor to be safe.