This melody is an old one dating from at least the 13th Century as a Gregorian Chant or Plainchant. Dies Irae translates as "Day of Wrath" but is sometimes more loosely translated as the "Wrath of God". The melody was used to sing some latin verses describing the Day of Judgement. It is often associated with death and was formerly included as part of a Requiem Mass. Mozart, Verdi and other composers of Requiem Masses have composed alternative melodies for the "Dies Irae". But the more ancient melody has been frequently used by other composers in their own compositions especially when their music has a macabre theme e.g. Hector Berlioz's Symphonie Fantastique, Franz Liszt's Totentanz (Dance of the Dead) or Sergei Rachmaninoff's Isle of the Dead and other works. Several film/TV composers have also adapted the theme (including Miklos Rozsa in "Young Bess" and "El Cid", Ennio Morricone in "The Mission", Basil Poledouris in "Conan the Barbarian" and Bernard Herrmann in "The Jar", an episode of "The Alfred Hitchcock Hour"), but most notably Wendy Carlos for the opening of the movie "The Shining" (and in turn referenced in Ready Player One). Because of this tradition among composers, the Dies Irae must qualify as the oldest piece of frequently quoted music.
This adaptation of the music is restricted to the first few lines of the ancient melody, since this part of the music is the most familiar from its frequent quotation. The arrangement is designed to be played with 2 hands in parallel on a keyboard or similar instrument, though other instruments can also play it. The music is in a free form with no strict time signature and can be interpreted in a number of ways. Since the music is choral in nature, the only significance of the slurs is to join notes which are used for the same syllable. The music is available as PDF Sheet Music, a MIDI file or an MP3 file (using an organ sound). Another Gregorian Chant on mfiles is the Pange Lingua.