Much like Melville's lengthy excursions from the plot of Moby Dick, Hugo indulges in long passages about the history of Notre Dame, the geography of the city, and the arcana of the hermetic knowledge ostensibly sealed up in the very stones of the city's buildings. I enjoyed these excursions much more than I did the detailed description of everything you never wanted to know about the sperm whale industry in the nineteenth century; in fact, the long chapters of Book III, divided into "Notre Dame" and "A Birds-eye View of Paris," are probably my favorite parts of the book.
Notre-Dame de Paris is a particularly curious specimen of this variety. Every face every stone, of the venerable structure is a page not only of the history of the country but also of the history of art and science....One might believe that there were six centuries between the doorway and those pillars. Alchemists themselves find in the symbols of the main entrance a satisfactory compendium of their science, of which the church of St.-Jacques-de-la-Boucherie was so complete a hieroglyphic....This central and fertile church is a sort of chimera among the ancient churches of Paris; it has the head of one, the limbs of another, the trunk of a third, and something of them all. (Modern Library ed., Catherine Liu transl.)Hugo breathes life into the medieval city and peoples it with characters that seem straight out of Chaucer -- the beautiful and otherworldly gypsy Esmerelda, frightful Quasimodo, ridiculous poet and goat-lover Gringoire, Sack Woman, and the hideously twisted Archdeacon Claude Frollo. One doesn't really feel great affection for any of these characters -- they seem too stylized in their various modes, like figures in a mystery play, but in their pitiable fates, they seem most human. That awful image from the perspective of Quasimodo as he views the hangman sliding down the rope to fall on Esmerelda's frail shoulders is truly sickening (I think I also remember this violent scene in one of the movie versions).
Any time Hugo is describing Quasimodo in the cathedral, the novel really soars -- it is the marriage of the Hunchback to his natural habitat and to his bells that is so moving. And here is the iconic scene of him snatching Esmerelda from her executioners the first time they attempt to hang her as a witch:
Suddenly, when the executioner's assistants were preparing to obey Charmolue's order, he climbed across the balustrade of the gallery, seized the rope with his feet, knees, and hands, glided down the facade like a drop of rain down a pane of glass, ran up to the two men with the swiftness of a cat that has fallen from a roof, knocked both of them to the ground with his enormous fists, and bore off the gypsy on one arm, as a girl would a doll. With one bound he was in the church, holding the young girl up above his head and shouting with a terrific voice, "Sanctuary! Sanctuary!" This was all done with the speed of lightning.