That Belli is supposed to have moved his audiences to tears, especially in L'Olimpiade, is reported in Edward Bernsdorf's Neues Universal-Lexikon der Tonkunst (Dresden: Schaefer, 1856: Vol. 1, p. 363 (Archive.org: online version)
books.google.com
Christian Felix Weiße (ed.): Gottlieb Wilhelm Rabener's Letters. Dyck, Leipzig, 1772, p. 249 f. (Google Books: online version
J.J. Winckelmann: Letter to Johann Michael Francke (1717-1775) of 30 September 1758 from Florence, cited from: J. Schultze, H. Meyer (eds.): Winckelmann's Werke. Bd 9: Briefe 1747-1761. Berlin: Schlesinger, 1824, p. 308 (Google Books: online version)
J.J. Winckelmann: Letter to Hieronymus Dietrich Berendis (1720-1783) of 21 February 1761 from Rome, quoted from: Johann Joachim Winckelmann: Briefe: Kritische-Historische Gesamtausgabe, Volume 2. Walter de Gruyter, Berlin 1954 (Google Books: online version (restricted preview)
Hans-Bertold Dietz: The Dresden-Naples Connection 1737-1763: Charles of Bourbon, Maria Amalia of Saxony, and Johann Adolf Hasse. In: International journal of musicology vol. 5, 1997, ISSN 0941-9535, pp. 95-144, here p. 124 (Google Books: online version (restricted preview)
J.J. Winckelmann: Letter to Baron Philipp von Stosch (1691-1757) of 6 February 1759 [recte 1760] from Rome - quoted from: J. Schultze, H. Meyer (eds.): Winkelmann's Werke. Bd 9: Briefe 1747-1761. Berlin: Schlesinger, 1824, p. 336 (Google Books; online version)
Moritz Fürstenau: Beiträge zur Geschichte der Musik und des Theaters am sächsischen Hofe während der Regierung August’s III. 1733–1763. Leipziger Zeitung – Wissenschaftliche Beilagen 1856, pp. 483–484 (Googl;e Books: online version)
