"The Requiem Mass in D minor was the last composition by Wolfgang Amadeus Mozart and was left unfinished at the Austrian composer's untimely demise at the young age of 35, on December 5, 1791, in Vienna, and completed by Franz Xaver Süssmayr. Under the supervision of Mozart's widow, Constanze, efforts to complete the Requiem began immediately after the composer's death. It was delivered to Count Franz von Walsegg, who had anonymously commissioned the piece for a requiem Mass to commemorate his wife's death anniversary, February 14."
