Franz Niemetschek’s legendary report that La clemenza di Tito was composed in 18 days was not seriously challenged until 1960, when Tomislav Volek published important archival materials relating to the chronology of the opera’s composition. Physical evidence from the autograph manuscript, including the remains of a fly squashed on the paper (probably by the composer in the heat of August), contributes to discrediting the hypothesis that Mozart’s work had begun before he signed his July 1791 contract for the opera.
This according to “The chronology of Mozart’s La clemenza di Tito reconsidered” by Sergio Durante (Music & letters, 80, no. 4 (Nov 1999): 560–594), where the evidence is described thus:
“On folio 114 of the autograph . . . a thick black spot in the shape of a cross is found. . . . On direct and close examination, the centre of the spot proves to host the remains of a fly (a kind of evidence not often found in music sources!). After a long reflection, my best guess is that the fly was smashed under the loose bifolium at the very time of composition, after it had unduly annoyed Mozart at work; he also provided a witty ‘service’ to the insect by marking a cross over it (‘requiescat’!); in any case, such was the force and determination of the action, combined with the gluing action of the ink, that the corpse is still stuck on the page after two hundred years of musicological investigations.” (p. 574)