We've got a poet-acrobat, high wire, and Beauty about to do a "death-defying leap" into his waiting (hopefully strong) arms. But there aren't any lions, clowns, or other notable signs that suggest this is your average circus. It's a circus of the poet's mind more than anything else. And as such, we can imagine that this place has probably got even neater things to offer than a bunch of clowns in a shrunken car.
Our acrobat has the cosmos on his side "where Beauty stands and waits with gravity" (lines 25-26). Bet you never saw that at a circus. And this circus never seems to end, what with Beauty's fair form being "eternal," and the fact that this is really all a metaphor for poetry-writing, which seems to be the poet-acrobat's lifetime calling. An endless circus? That sounds… exhausting.
And to top it all off, he's risking "absurdity and death" throughout it all. No nets, no elephants, no promises.