From Poe's "Philosophy of Composition":

I made the bird alight on the bust of Pallas, also for  the effect of contrast between the marble and the plumage — it being understood that the bust was absolutely suggested by the bird — the bust of Pallas being chosen, first, as most in keeping with the scholarship of the lover, and, secondly, for the sonorousness of the word, Pallas, itself.

Read the Full Text.