It's a rule : all big poems have to be modelled mathematically on the architecture of a building (or part of a building). For Dante it was the mosaics in the chapel in the Ravenna cathedral (there's a good book on the numerology of this). For Pound it was the Malatesta crypt. For Crane, of course, it was... you know.

I modelled the middle book of Forth of July (The Grassblade Light) on the Castel del Monte.

(Frederick II had many negative qualities. But in my poem he & his Castel represent a principle which both Dante & Roger Williams stood for : the separate, dual & independent spheres of church & state.)