Dante Alighieri, Baroliniano. "Purgatorio 21". Digital Dante, Commentary & Context. Columbia University. Archived from the original on December 19, 2016. Retrieved December 13, 2016.
crystalinks.com
"Statius". Crystalinks. Retrieved December 13, 2016.
Dante Alighieri, Baroliniano. "Purgatorio 21". Digital Dante, Commentary & Context. Columbia University. Archived from the original on December 19, 2016. Retrieved December 13, 2016.