The next-to-last sentence of "The Cask of Amontillado" ("For the half of a century no mortal has disturbed them") is an example of denouement, but what's the significance to the story?
This is the sentence after he says "I forced the last stone into its position; I plastered it on top. Against the new masonry I re-erected the old rampart of bones."
The next-to-last sentence of Edgar Allan Poe's classic "The Cask of Amontillado" does indeed serve as the denouement (the resolution) of the short story.
For the half of a century no mortal has disturbed them.
The simple line sums up Montresor's act of revenge against Fortunato, revealing that the murder that Montresor committed had been a perfect crime: Fortunato's body was never found, and Montresor was never punished for his act. These were two of Montresor's goals as stated early in the story, that
I must not only punish but punish with impunity. A wrong is unredressed when retribution overtakes its redresser. It is equally unredressed when the avenger fails to make himself felt as such to him who has done the wrong.
Montresor's careful planning succeeded in luring Fortunato into a final resting place in which his body would never be discovered. Montresor's revenge was complete. The line in question shows that 50 years have passed and that Montresor must now be an old man, perhaps confessing his sin to a priest or close family member.