Achaea is the term that refers to the plane of existence upon which Sapience, Ulangi, Polyargos, and other landmasses reside. The Solstar, the Moon, the celestial triad of Noxtra, Somnustra, and Lunastra, as well as other unnamed stars make up the viewable heavens.
There was once much contention as to the shape of the land upon which Sapience rests, some claiming it was round, others claiming it was flat. The Wall of Power, an enormous wall of energy that blocks passage at a certain distance in all directions, made it impossible for mortals to explore further and find the truth for themselves. Fortunately, the argument was settled by Sarapis, when He proclaimed that Achaea was "created in imitation of an n+1 Calabi-Yau space."