This scene is important because this is when Montresor convinces Fortunato to go have drink with him down in the catacombs. This is when Fortunato was drunk and Montresor saw him and took advantage of that. He led him to the catacombs which had poisonous nitre in them. This was significant because it was the first step in his evil plot.
Montresor lures Fortunato to the dark creepy catacomb and keeps insisting that they turn back because of the poisonous nitre. But instead Montresor keeps drinking more wine and continues deeper in the catacombs. Montresor keeps urging Fortunato to go back but this only makes Fortunato want to keep going. Fortunato also keeps inhaling the nitre which keeps making him more sick.
As Montresor and Fortunato keep going further and further, the nitre get thicker and Fortunato gets sicker. Montresor also reveals his family motto which means that No one attacks me with impunity. This shows that Montresor wants revenge on Fortuanto for insulting him. There is also moisture dripping on the bones from the nitre which foreshadows that Fortuanto is going to die from the nitre.
Montresor chains up Fortunado and Fortunado finally realizes what Montresor was planning to do. Fortunado was in shock when Montresor chained him up and he stilled asked for the Amontillado. This scene is important because this is what the whole story was leading up to. Montresor finally shows what he was planning to do and that was to chain him up and just leave him.
After Montresor chains fortunado up, he begins covering up the niche where he is. Fortunado screams for him to stop. After Montresor hears him scream he hesitated and trembled. This scene is significant because after Montresor was finished building a wall over him, he could hear him talking to him and Montresor wanted to be with him.
Montresor starts finishing up the wall. He starts to hear Fortunado talking to him and he then heard his bells jingle. Montresor's heart grew sick from this and lays the last stone. He then leaves Montresor behind and doesn't tell any one about it until 50 years later.