Why is the description of Montressor's family crest important?What literary elements are used?

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bullgatortail eNotes educator| Certified Educator

Montressor is proud of his family's heritage, and it is apparent that Fortunato's "insult" concerned a personal slight to his name. As Montressor leads Fortunato to his final resting place, the doomed man comments on the "extensive" nature of the catacombs.

    “The Montresors,” I replied, “were a great and numerous family.”
    “I forget your arms.”
    “A huge human foot d'or, in a field azure; the foot crushes a serpent rampant whose fangs are imbedded in the heel.”
    “And the motto?”
    “Nemo me impune lacessit.”
   
“Good!” he said.

The Latin interpretation of the motto, to "Punish with Impunity," is acceptable to Fortunato, but he will soon find that Montressor lives by the credo. For it is exactly in this manner that he will kill Fortunato. When he leaves Fortunato to die within the walled recess, hidden so no one will ever find him, he lives up to the family motto: He successfully punishes Fortunato without suffering the consequences of the crime.

There are several layers of irony here: One, is that Fortunato unknowingly approves of the motto; secondly, he walks willingly to the spot where he helps Montressor fulfill his goal; and, finally, Fortunato's bones will soon be intermixed with those of the family he has insulted. Additionally, Poe foreshadows the outcome by including this dialogue between the two men