The earliest composition by Josef Mysliveček (1737–1781), evidently written before he left for Italy (1763), was proved to be the occasional congratulatory cantata Alceste e Fileno, to an anonymous, allegorical pastoral text. The unanimous dating of the composition before 1757 is helped by a dedication, on the occasion of the election of the Zbraslav Cistercian Monastery abbot Desiderius Andres (in function between 1757 and 1770). The unique, undated copy of the cantata, in the music collection of the Osek Cistercian Monastery in north-western Bohemia, (deposited in the National Museum, Czech Museum of Music in Prague, shelf-mark CZ Pnm XXXII A 62) and procured by the local choirmaster Leonard Dont is presumably affiliated to the original source (perhaps the dedication autograph), from the Zbraslav music collection, today considered to be lost. The opening sinfonia, surviving in five other individual copies, suggests further hypotheses. It survives, amongst others, in the Waldstein music collection, in a group of Mysliveček’s early sinfonies, which are believed (by J. Čeleda, and R. Pečman) to be identical with the composer’s first works, which, according to the obituary, written by J. M. Pelcl, the composer had performed in an unspecified Prague theatre – probably, in fact, in the Waldstein Palace. The dating of the piece suggests that at the age of twenty, J. Mysliveček had already composed, and left Prague with certain compositional skills.