We’ve said it before and we’ll say it again: Yeats has some strange symbolism going on in this poem. He actually spent some serious time developing a whole code of symbols, which he used in almost all of his poetry. In A Vision, a philosophical tract written by good ol’ W.B., he explains it all. That is, if there can be any explanation for the stuff that he’s coming up with! There’s even a website devoted to his system: www.yeatsvision.com.
Yeats was obsessed with Byzantium. Why shouldn’t you be? Here’s a way to get started: check out the Byzantine history web page from Fordam University.