July: Mozart completes the cantata Die ihr des unermeßlichen Weltalls (K. 619).
mid-July: A messenger (probably Franz Anton Leitgeb, the count's steward) arrives with note asking Mozart to write a Requiem mass.
mid-July: Commission from Domenico Guardasoni, impresario of the Prague National Theatre to compose the opera, La clemenza di Tito (K. 621), for the festivities surrounding the coronation on September 6 of Leopold II as King of Bohemia.
5 December – 10 December: Kyrie from Requiem completed by unknown musician (once identified as Mozart's pupil Franz Jakob Freystädtler, although this attribution is not generally accepted now)
21 December: Joseph Leopold Eybler receives score of Requiem from Mozart's widow, Constanze, promising to complete it by mid-Lent (mid-March) of next year. He later gives up and returns the score to Constanze, who turns it to Süssmayr to complete.
After 1791
Early March 1792: Probably the time Süssmayr finished the Requiem.
2 January 1793: Performance of Requiem for Constanze's benefit arranged by Gottfried van Swieten.
Early December 1793: Requiem is delivered to the Count.
14 December 1793: Requiem is performed in memory of the count's wife in the Cistercian Neukloster Abbey at Wiener-Neustadt.[3]
14 February 1794: Requiem is performed again in Patronat Church Maria Schutz in Semmering.
1800 or later: Walsegg receives leaves 1 through 10 of the autograph (Introitus and Kyrie).
Autumn 1800: Abbé Maximilian Stadler compares all known manuscript copies (including Walsegg's) and editions of the score, notes copying errors, and determines precisely which parts of the Requiem were written by Mozart.
After 1802: Abbé Stadler receives leaves 11 through 32 (Dies irae to Confutatis) of Mozart's Requiem autograph from Constanze. Later Eybler would receive leaves 33 to 46, the Lacrymosa through Hostias.
17 September 1803: Süssmayr dies of tuberculosis and is buried in an unmarked grave in the St. Marx Cemetery.
1825: Gottfried Weber writes an article in the music journal Cäcilia calling Mozart's Requiem a spurious work.
11 November 1827: Count Walsegg dies. Karl Haag, a musician formerly in Walsegg's service, receives his score (Mozart's autograph of the Introitus and Kyrie; the rest a copy by Süssmayr) and when he dies, he wills it to Katharina Adelpoller.
1831: Abbé Stadler gives the leaves of the Requiem autograph in his possession to the Imperial Court Library.
1833: Eybler suffers a stroke while conducting a performance of Mozart's Requiem. The leaves of the Requiem autograph in his possession are turned over to the Imperial Court Library.
8 November 1833: Abbé Stadler dies.
1838: Count Moritz von Dietrichstein asks Nowack, formerly an employee of Walsegg, to search among Haag's possessions for six Mozart string quartets that may have been given to Walsegg. Nowack does not find them but discovers Walsegg's score of Mozart's Requiem. The Imperial Court Library pays Adelpoller 50 ducats for the score.
