Several points of interest: the escape from an impregnable prison is a trope of Romantic fiction, Casanova's famous escape over the roof (leads) of the Venetian prison may be the immediate inspiration. But the patient digging away with a primitive tool reminds me of that pan-European Gothic blockbuster, Charles Henry Maturin's Melmoth the Wanderer (1820), a book that Balzac had recently written a sequel to (Melmoth reconcié, 1835). Of course, Dumas's subsequent Comte de Monte-Cristo (1846) is the most famous of the digging-out-of-prison stories, and such prison escapes or near-escapes are a staple in Dumas (La Dame de Monsureau, La Reine Margot, and L'Homme au masque de fer.)
The unusual device here is that the hero is clued into his (dead) predecessors' nearly-completed excavations by his ability to read Arabic graffiti left by a former cell occupant, a skill the hero picked up as the scion of a merchant family in the Mediterranean.
The nameless narrator is a poor middle-class intellectual, a scientist who lives among the working classes of the Marais. blending in well enough to be able to closely observe the working classes, which he does "scientifically".
The scientific analysis of the working classes by a sympathetic intellectual -- this is the revolution of nineteenth century literature. He tells us at one point that the story of the blind Venetian is just one among many that the has gathered. Like Balzac himself, who could blend in with al ranks of society – as portrayed by literal invisibility in La Canne de M. de Balzac (also 1836) –, the narrator acts as a kind of "nobleman in disguise" figure, another staple of romantic tale-telling.
Une seule passion m'entraînait en dehors de mes habitudes studieuses ; mais n'était-ce pas encore de l'étude ? j'allais observer les mœurs du faubourg, ses habitants et leurs caractères. Aussi mal vêtu que les ouvriers, indifférent au décorum, je ne les mettais point en garde contre moi ; je pouvais me mêler à leurs groupes, les voir concluant leurs marchés, et se disputant à l'heure où ils quittent le travail. Chez moi l'observation était déjà devenue intuitivel
A single passion pulled be away from my studious habits, but wasn't it even more study? I observed the manners of the faubourg, its inhabitants and their characters. As badly dressed as the workers, indifferent to decorum, I did not put them on guard against me; I could join in their groups, see them conduct business, and argue at quitting time. In me, observation had already become intuitive.