Coleridge always claimed that Kubla Khan came to him as a dream-vision, and that he never put any conscious thought into it. He also claimed that there was a lot more of it in the dream, but that he was interrupted halfway through writing it by a businessman from Porlock, and that as a result it was unfinished. This is clearly a bunch of nonsense. For a start, the ending is definitely an ending. And secondly the poem contains so many intricate details that the idea that anybody dreams like that is, frankly, preposterous. Fifty-four lines of perfect rhymes would be astonishing by anybody's standards.
But what I happened to notice today was the alliteration. It's all over the poem, of course, "A mighty fountain momently was forced" and "Five miles meandering with a mazy motion". But I noticed that, usually, it's concentrated on the last two words of the line. Take the opening:
In Xanadu did Kubla Khan
A stately pleasure-Dome Decree:
Where Alph, the sacred River, Ran
Through caverns Measureless to Man
Down to a Sunless Sea.
It's regular enough that it's almost part of the verse form: the iambic tetrameter with alliterative ending. Then it disappears for the next twenty lines before starting again in the second half of the poem. In total 15 of the 54 lines end alliteratively. This can't be coincidence. A quick look at Recantation, which is the next poem in my edition of Coleridge, doesn't have a single one in the first thirty lines.
To work thus did the Khan commute.