See upon this subject, Cancellieri, Osservazioni Sopra l’Originalità di Dante ;⁠—Wright, St. Patrick’s Purgatory, an Essay on the Legends of Purgatory, Hell, and Paradise, current during the Middle Ages ;⁠—Ozanam, Dante et la Philosophie Catholique au Treizième Siècle ;⁠—Labitte, La Divine Comédie avant Dante , published as an Introduction to the translation of Brizeux;⁠—and Delepierre, Le Livre des Visions, ou l’Enfer et le Ciel décrits par ceux qui les ont vus . ↩

The action of the poem begins on Good Friday of the year 1300, at which time Dante, who was born in 1265, had reached the middle of the Scriptural threescore years and ten. It ends on the first Sunday after Easter, making in all ten days. ↩