- Purgatorio, part of the Divine Comedy by Dante. Multiple English translations exist.
- "Purgatory," by Carlton Joseph Huntley Hayes in Encyclopædia Britannica (11th ed., 1911)
- "Purgatory," in Catholic Encyclopedia, (ed.) by Charles G. Herbermann and others, New York: The Encyclopaedia Press (1913)
- "Purgatory," in The Encyclopedia Americana, New York: The Encyclopedia Americana Corporation (1920)
- "Purgatory," in Collier's New Encyclopedia, New York: P. F. Collier & Son Co. (1921)