"I was saying, sire, that perhaps you are right—that the hour of the people here has not yet come."
Louis fixed on him his piercing eye. "And when will that hour arrive?"
"You will hear it strike."
"By what clock, pray?"
Coppenole, with a grave but tranquil look, drew the King close to the window. "Listen, sire. Here is a castle keep, there a bell tower, canon, bourgeois, soldiers. When the bell tower buzzes, when the cannon roar, when the keep collapses with a mighty crash, when the bourgeois and the soldiers shout and slay one another, then the hour will have struck."
The face of Louis XI became gloomy and thoughtful. For a moment he was silent; then he patted the thick wall of the tower as though it were the flank of a favorite charger. "Oh no!" he said. "You will not fall so easily, my good Bastille!" (X.V.232-2237)
For readers in the 1830s, it would have been impossible to miss the ironic reference to the sturdiness of the Bastille, which was attacked and destroyed in 1789 at the outset of the French Revolution because it represented the monarchy's abusive state power (that's what it represents in this scene too—remember the prisoner in the box?).
So there's that important bit of history. But how is this conversation at all relevant to the story? Why does Hugo refer to events from 1789 in a story set in 1482? Well, by commenting on how things were in 1482, Hugo is also able to say things about the France of his own time and about what exactly those changes mean in a bigger historical context. Also, it's sometimes safer and more effective to say dangerous things about your own time if you cloak them in historical garb.