starts with a foghorn sound that is known as the "Enigma horn". After the foghorn, Sandra Cretu starts talking and invites the listener to relax and take a deep breath, while an environmental soundscape plays in the background. "The Principles of Lust" track employs a drumbeat throughout similar to the R&B 1989 song "Back to Life (However Do You Want Me)" by Soul II Soul, flute synth lines, and Cretu's whispers and "orgasmic breathing" that mark the song breaks. The first part, "Sadeness", includes a Gregorian chant taken from the track "Procedamus in pace!" from the 1976 album Paschale Mysterium by Capella Antiqua München. It also includes contributions from Fabrice Cuitad and Peterson. The song's French lyrics are a quizzical look at, and defense of, the 18th-century writer Marquis de Sade, who was notorious for writing literature delving into themes of sexual violence and domination. "Callas Went Away" was written solely by Michael Cretu, and samples Maria Callas's singing. "Mea Culpa" was written by Cretu and Fabrice Cuitad and is a follow-up to "Sadeness". Like "Sadeness", "Mea Culpa" samples Gregorian chant from the Capella Antiqua München and thus evokes the same atmosphere. The song's theme "centers around guilt", according to the official Enigma website. "The Voice & the Snake", written by Cretu and Peterson, is based on the Book of Revelation. "Knocking on Forbidden Doors" was written solely by Cretu. The "Back to the Rivers of Belief" track's three songs were mainly written by Cretu, with the song "The Rivers of Belief"—which centers around the Indian river Ganges and differs from the other songs in being more soulful—including contributions from Fabrice Cuitad. Singles Four songs from MCMXC a.D. were released as singles. "Sadeness (Part I)", known as "Sadeness" in the album and the first part of "The Principles of Lust" track, was released as the lead single on 1 October 1990. The single has sold at least 7 million copies worldwide, and was the fastest German single to reach number one, the week of 12 November 1990. The Los Angeles Times reported that the single reached number one in at least 14 other countries. "Mea Culpa (Part II)", known as "Mea Culpa" in the album, was released as the second single on 17 April 1991, and reached number seven on both the German charts and on the Billboard Dance Club Songs chart. The song charted at number four in France,