Poe's own fear of being buried alive is one of the most important themes in "The Cask of Amontillado." To project this fear on others, he stresses the dark and hostile environment of the catacomb, making what should be a simple, nonthreatening wine-cellar into a frightening tomb:
We had passed through long walls of piled skeletons, with casks and puncheons intermingling, into the inmost recesses of the catacombs.
We passed through a range of low arches, descended, passed on, and descending again, arrived at a deep crypt, in which the foulness of the air caused our flambeaux (torch) rather to glow than flame.
(Poe, "The Cask of Amontillado," eNotes eText)
The fear of being confined is called claustrophobia, and is a common fear. The damp walls, with their piled skeletons and sheen of nitre, are meant for confining the dead, not housing the living. The air itself is so thick with humidity and dust that it almost puts the torch out. As the air weighs heavy on their lungs, and the walls seem to press in, Montresor's plan becomes evident, and Poe uses Fortunato's mental deterioration to show his terrible fear, first screaming, and then laughing madly in disbelief.