Requiem, for soloists, chorus, orchestra and organ in C minor

The Requiem in D minor, K. 626, is a Requiem Mass by Wolfgang Amadeus Mozart (1756–1791). Mozart composed part of the Requiem in Vienna in late 1791, but it was unfinished at his death on 5 December the same year. A completed version was delivered to Count Franz von Walsegg, who had commissioned the piece for a requiem service on 14 February 1792 to commemorate the first anniversary of the death of his wife Anna, who had died at the age of 20 on 14 February 1791. The autograph manuscript shows the finished and orchestrated movement of the Introit in Mozart's hand, and detailed drafts of the Kyrie, the Sequence (the latter including the first eight bars of the Lacrimosa), and the Offertorium. First Joseph Eybler and then Franz Xaver Süssmayr filled in the rest, composed additional movements, and made a clean copy of the completed parts of the score for delivery to Walsegg, imitating Mozart's musical handwriting but clumsily dating it "1792." It cannot be shown to what extent Süssmayr may have depended on now lost "scraps of paper" for the remainder; he later claimed the Sanctus and Benedictus and the Agnus Dei as his own. Walsegg probably intended to pass the Requiem off as his own composition, as he is known to have done with other works. This plan was frustrated by a public benefit performance for Mozart's widow Constanze. She was responsible for a number of stories surrounding the composition of the work, including the claims that Mozart received the commission from a mysterious messenger who did not reveal the commissioner's identity, and that Mozart came to believe that he was writing the Requiem for his own funeral. In addition to the Süssmayr version, a number of alternative completions have been developed by composers and musicologists in the 20th and 21st centuries. At least 19 conjectural completions have been made, eleven of which date from after 2005.