Montresor states that Fortunato is wearing a "tight-fitting" jester's costume when he encounters him carousing on the street. Montresor has a rapier concealed under his cloak. He reveals this fact for the first time when Fortunato begins screaming for help.
A succession of loud and shrill screams, bursting suddenly from the throat of the chained form, seemed to thrust me violently back. For a brief moment I hesitated, I trembled. Unsheathing my rapier, I began to grope with it about the recess...
Montresor's main problem is to get Fortunato to come to his palazzo and down into the wine cellar without being recognized by anyone on the streets as Fortunato's companion. Montresor is armed; Fortunato must be unarmed because there would be no place to conceal a weapon in a tight-fitting costume. Montresor could simply murder Fortunato at the foot of the steps. Then he would have to bury him somewhere under the palazzo. This sounds like a hackneyed plot. How many men in stories and novels have murdered people and buried them in their cellars?
The trip through the catacombs makes Poe's story most interesting. Chaining Fortunato inside the narrow niche and building a wall to conceal him also add interest. Without such details the plot would lack some of its best effects, such as Fortunato's screaming for help and pleading for mercy, and the story would probably not have been remembered as long as it has.