Haven is a Pod Age at this time.
The Torus Age, meanwhile, is a Guild Classic. Spire is either a Classic or a personal Age.- Please Elaborate. Not all of us know what "Pod", "Guild Classic", or "Classic" Ages are.
- Pod Ages are Ages where you link to a safe pod from where you can view the wildlife. Negilahn, Dereno, Payiferen, and Tetsonot are all pods on the same Age. Guild Classics are Ages officially regarded as the greatest ever Written. Yakul from Book of Tiana was one such, but its fate is unknown.
Spire is a fragment.
Atrus' explanation of "wind-formed" stairs and archways is implausible enough before you take into account the decorations and architectural elements the "wind" apparently carved around the archways. Sirrus didn't add them either; they were already there in the flashbacks. So here's another explanation: The whole floating island is part of something larger that is (or used to be) populated. Possibly some kind of floating city that orbited the planet, or even launched into orbit by some disaster.
The "has never had any inhabitants" might well have come from an Unreliable Narrator, since Atrus never investigated the Age in detail.
- Better yet the natives are in fact Air Elementals and thus aren't actually inhabitants with Spire itself being Skywall the Elemental Plane of Air!
Spire the planet has electromagnetic life forms that maintain the electrostatic fields keeping the castles from plunging down below the habitable region.
