In the excerpt below, the prominent figure of speech in these liens is alliteration.
Alliteration is a literary device which is used by the writer to emphasize something that he/she wants to express. To spot an alliteration, it begins with the same consonant sound.
alliteration in the above excerpts are, "Xanadu did"
"dome decree."
In these lines, the poet describes the "stately pleasure dome" in Xanadu.