The Hunchback of Notre Dame uses the history of the Middle Ages and the structure of the Notre Dame cathedral to express its major themes. Notre Dame is the geographical and moral center of Hugo's fictional Paris. The cathedral inspired Hugo to write the novel and encouraged his life long passion for Gothic art and architecture. Hugo was also a scholar of medieval Christianity and used the history of its churches, martyrs, and saints as a backdrop for the novel's action. The French title of the novel is Notre Dame de Paris, emphasizing Notre Dame's role as a symbol of the city. Not only does most of the novel's action unfold inside or around the cathedral, but from the top of its towers, Claude Frollo and Quasimodo can spy on virtually anyone in the entire city. Architecturally, it is an "amalgamation" that mirrors Quasimodo's own deformities.
At the time Hugo was writing, Notre Dame was falling apart, and there was very little respect for its architecture. Nothing had been done to repair the damage done to it during the French Revolution. However, the Romantic literary movement seized upon the cathedral as a symbol of France's glorious Christian past. For example, in Eugène Delacroix's famous depiction of the 1830 Revolution, Liberty Guiding the People, the two towers of Notre Dame can be seen in the background, evoking the mythic presence of Paris. Hugo greatly admired this painting, striving to represent Notre Dame as the cultural and political center of Paris. At the Romantics' urging, Parisians gradually came to see Notre Dame as a national monument and symbol of France. By 1845, a massive restoration program of Notre Dame began.
The novel is primarily concerned with the theme of revolution and social strife. Hugo was profoundly concerned by the class differences that set the 1789 French Revolution in motion. Discord between the Clergy, Nobility, and the Third Estate (a middle class of artisans, craftsmen, and intellectuals) toppled the monarchy and established a republican government that no longer recognized the special privileges of the aristocracy and the Church. Writing during the July 1830 Revolution, Hugo was more conscious of class divisions than ever. For example, as the vagabonds prepare to march, Clopin declares: "Trade is incompatible with nobility." Consequently, the vagabonds' assault on Notre Dame represents an example of historical foreshadowing that would remind Hugo's contemporary readers of the 1789 storming of the Bastille. The fact that Louis XI is in the Bastille when the vagabonds attack further emphasizes this historical reference. The fact that every character is an orphan also evokes the deterioration of the feudal system. French society was viewed as one giant happy family under the Bourbon kings and the breakdown of this family unit in the novel foreshadows the civil wars that would divide the nation in two beginning in 1789.
The theme of determinism also dominates the novel, especially in the scene where Frollo watches a fly get caught in a spider's web. Many characters in the novel do not believe in free will. For example, when Pierre Gringoire follows La Esmerelda he "resigns his free will" and accepts any direction that she chooses. Similarly, Frollo believes that all actions have been predetermined and that nothing can stop him from catching La Esmerelda. Just as the fly is bound to get caught in the spider's web, he thinks that she is bound to fall into one of his traps. He thus uses this example of "fatality" to justify his actions since nothing he or anyone else can do will change the predetermined outcome. As he warns his associate, one should never "meddle with fatality." Hugo acknowledges that fate plays a powerful role in the novel, but implies that free will is possible. Hugo suggests that Frollo's deterministic attitude and resignation of free will is what allows him to become such a horrible person. Hugo suggests that we must all exercise our free will to retain our sense of morality and the responsibility for our actions.