Felice De Filippis (ed), Cento anni di vita del Teatro di San Carlo, 1848–1948, Naples, Teatro San Carlo, 1948, p. 213; Casaglia, Gherardo (2005). "Guglielmo d´Aquitania,18 October 1942". L'Almanacco di Gherardo Casaglia (in Italian).
archive.org
Paris, Duchesne, 1768, p. 182 (accessible online at Internet Archive).
De probatis sanctorum historiis, partim ex tomis Aloysii Lipomani, doctissimi episcopi, partim etiam ex egregiis manuscriptis codicibus, quarum permultae antehac nunquam in lucem prodiēre, nunc recens optima fide collectis per f. Laurentium Surium Carthusianum, Cologne, Geruinum Calenium & haeredes Quentelios, 1570, I, pp. 925–948 (accessible online at Google Books).
On this subject see the remarks in the authoritative History of the Religious and Military Monastic Orders by Pierre Helyot and Maximilien Bullot, namely that there was practically no "Duke of Aquitaine, beginning with William 'Towhead'" who had not been confused with Saint William of Maleval (even though, to be perfectly accurate, William "Towhead" was the nickname of the third not the second Duke of Aquitaine). The work of the two French authors only appeared in Italian translation a few years after the premiere of Pergolesi's dramma sacro: Storia degli ordini monastici, religiosi e militari e delle congregazioni secolari (...), Lucca, Salani, 1738, VI, p. 150 (accessible online at Google Books).
comune.modena.it
According to another reading of the libretto it is possible that it was William who blinded himself as a form of self-imposed penance. This was the interpretation adopted by a student production of La conversione staged on 14 July 2011 at Carpi, in the cloisters of the Convent of San Rocco, conducted by their teacher Mario Sollazzo, directed by Paolo V. Montanari, with the Vocal Instrumental Ensemble of the Istituto Superiore di Studi Musicali "O. Vecchi – A. Tonelli", a music school located at Modena and Carpi (cf. Comune di Modena WebsiteArchived 2016-12-20 at the Wayback Machine).
persee.fr
Gustavo Rodolfo Ceriello, Comedias de Santos a Napoli, nel '600 (with previously unpublished documents); "Bulletin Hispanique", Volume 22, n° 2, 1920, pp. 77–100 (accessible online at Persée).
According to another reading of the libretto it is possible that it was William who blinded himself as a form of self-imposed penance. This was the interpretation adopted by a student production of La conversione staged on 14 July 2011 at Carpi, in the cloisters of the Convent of San Rocco, conducted by their teacher Mario Sollazzo, directed by Paolo V. Montanari, with the Vocal Instrumental Ensemble of the Istituto Superiore di Studi Musicali "O. Vecchi – A. Tonelli", a music school located at Modena and Carpi (cf. Comune di Modena WebsiteArchived 2016-12-20 at the Wayback Machine).