The 120 Days of Sodom

 was a book written by the Marquis de Sade. (PROSE: The Man in the Velvet Mask, The Adventuress of Henrietta Street)

He began writing it in 1783 while imprisoned in the Vincennes dungeons, (PROSE: The Adventuress of Henrietta Street) where he was known only as "Monsieur le 6". (PROSE: The Man in the Velvet Mask, The Adventuress of Henrietta Street) In the alternate Paris of the World Machine, de Sade feared that the published version of Les 120 Journées de Sodome was much weaker than his lost original draft. (PROSE: The Man in the Velvet Mask)

The book described an endless list of sexual perversions, which the Monsieur attributed to the corrupt rulers of France. While his contemporaries regarded it as the "most blasphemous, bloodthirsty work of pornography ever written", later generations appreciated it as the first work of clinical psychosexuality.

It was published in the same year as, and invited comparison with, the Eighth Doctor's book The Ruminations of a Foreign Traveller in His Element. (PROSE: The Adventuress of Henrietta Street)