Symbolism, Imagery, Allegory
The narrator observes a crack in the mansion upon his arrival to the Usher estate. Since he’s just mentioned that “The House of Usher” refers both to the family and the building, we should have an eye out for symbolic connections between the two. And indeed, we can see this small fissure as representative of a disruption in the unity of the family, more specifically, between Madeline and her brother. This is the disruption that ultimately tears the family – and the mansion – to pieces.