According to Mozart’s own handwritten catalogue of his works, the Verzeichnüßaller meiner Werke vom Monath febrario 1784 bis Monath 1 ( as the gap between ‘Monath’ and ‘1’, representing an unspecific future date, shows, Mozart, in February 1784 expected to live well into the nineteenth century), his Masonic Mourning Music was written in July 1785 to commemorate the deaths of two of his Masonic brothers, Georg August von Mecklenburg-Strelitz and Franz Esterházy von Galántha: ‘Maurerische TrauerMusick bey dem Todfalle der Brbr: Mecklenburg und Esterhazy. — 2 violini, 2 viole, 1 Clarinett, 1 Baßethorn, 2 oboe, 2 Corni e Baßo, incipit on f. 4r [Masonic Mourning Music on the deaths of Brothers Mecklenburg and Esterhazy. — 2 violins, 2 violas, 1 Clarinet, 1 Bassethorn, 2 oboes, 2 Horns and Basso.’ (f. 5v).
Both were commemorated at a memorial service on 17 November at Mozart’s lodge, ‘Zur gekrönten Hoffnung’ (Crowned Hope). However, not only in light of the date of the memorial but also, and more importantly, the death dates of von Mecklenburg-Strelitz and Esterházy (6 and 7 November 1785, respectively), Mozart’s dating of July seems to be incorrect. It has been speculated that the work existed in an earlier, now-lost iteration for chorus and orchestra that was performed on 12 August at the lodge ‘Zur wahren Eintracht’ (True Concord) to celebrate the induction of a new member.
 See Philippe Autexier, ‘Wann wurde die Maurerische Trauermusik uraufgeführt?’, Mozart-Jahrbuch 1984, 56-58, and Heinz Schuler, ‘Mozarts “Maurerische Trauermusik” KV 477/479a: Eine Dokumentation’, Mitteilungen der Internationalen Stiftung Mozarteum 40/1-4 (1992), 46-70.