Several parallels are made between the House of Usher and its occupant; too many, in fact, to be accidental. Why has Poe linked the two?

The House of Usher signifies the whole family or at least what was left of them. Both Madeline (before she "died") and Roderick sufferer from strange illnesses. Poe’s subtext is that there is some creepy incest stuff going on, "...The stem of the Usher race...had put forth, at no period, any enduring branch; in other words, that the entire family lay in the direct line of descent, and had always, with very trifling and very temporary variation, so lain." Roderick comes to believe that the mansion is directly related to his malady," He believes that somehow the mansion controls his behaviour, and what eventually will become of him. “The decaying state of the mansion parallels the decaying state of Roderick. I think Poe was looking to create a very literal sense of artistic unity. He wanted to present a physical structure that would manifest the tragedy of this family. It's like the DNA of the house itself was faulty hence the subtext of incest. As Madeline makes her zombie entrance and Roderick, more or less, melts away, it somehow makes sense that this very sick house finally self-destructs putting an end to this whole creepy family.