Wow! This is a great question. I love "Sailing To Byzantium" and, as with most Yeats poems, there is so much complexity that we will probably never uncover there. Great connection with Aeneas' golden bough! This is very likely a reference to the Aeneid to evoke deeper symbolism.
This passage in the Aeneid describes Aeneas plucking the branch from an oak tree to return to the Sybil. The Sybil herself is deeply connected with the mysticism Yeats is evoking in his poem, but the singing of the bird on the golden bough reflects the birds which Aeneas follows to find the branch. Later, after Aeneas has returned to the Sybil with the golden bough, he enters the underworld which is called "The Birdless Place." Perhaps Yeats is saying that our frailty cannot allow us to sing after death, and that we must be plated in gold if we want to live until the end of time. But his poem also seems to suggest that to forego death is in itself a fruitless undertaking—much like the branch of gold which will never grow, however beautiful it might be.
There's 100% deeper meaning there too—what do you think? How does the Sybil relate to the branch or Yeats' poem? How does the funeral that happens right before Aeneas' entrance into the underworld connect to the bough? What does the analogousness of gold with purity and worthiness in the Aeneid have to do with Yeats' description of Byzantium? Is the whole poem referencing this scene (sailing to Byzantium compared to crossing the Styx)?
Thank you for the question! I enjoyed responding to it.
I used the Sarah Ruden translation of Vergil's Aeneid to respond to this question.
