untransformed factionalism, Sordello ends up as the tour guide to the Valley of the Negligent Princes, where factionalism no longer holds sway. All three of these characters illustrate the concept of back illumination; when we come to this point in Purgatorio, we more fully understand what we have previously read in Inferno. In canto 9, Dante has the first of his three dreams on Purgatory. Night falls three times during his climb, and, just before each subsequent dawn, Dante has a transitional dream that looks back to the previous day's activity and ahead to that of the next day. In canto 9, Dante dreams that a gigantic eagle snatches him and swoops him off, and he awakens to find that during his sleep St. Lucy has transported him from the Valley of the Princes to the Gate of Heaven. In a very literal way the dream provides a transition, from one to another day, from one to another level of Purgatory, and from one to another physical locale. The dream of the siren (or of Serena) in canto 19 also provides a transition, this time to the upper three terraces of Purgatory where souls do penance for their self-indulgent instincts. Dante here dreams of an old woman who seems hideously ugly, until she is converted by Dante's glance into a beautiful and seductive young woman, the same Siren who attracted Ulysses and who continues to lure other voyagers to their destruction. A heavenly lady then calls upon Virgil to do something, and he rips open the belly of the Siren, exposing the ugliness and stench below the attractive-seeming surface. The dream points, not only forward to the next three terraces, but also backward to the discussion of love and freedom in cantos 16-18. Virgil, as a figure of Reason, guards the threshold of consent and protects Dante from the deception of his senses. Finally, in canto 27, Dante dreams of Leah and Rachel, providing thereby a transition to the earthly paradise up above. In the Book of Genesis, Jacob had been t...
