Great Wheel

In the Great Wheel cosmology , the Prime Material plane consisted of an infinite expanse filled with a fluid known as phlogiston , within which floated immense crystal spheres , each enclosing an entire system of one or more worlds. Specific conditions varied greatly from one crystal sphere to another, but they were all considered to be part of the same plane.

Outer Planes is a collective term used to describe a subset of the known planes of existence in various cosmology models. The term refers to the placement of the planes being the outermost concentric sphere that made up the multiverse in the Great Wheel cosmology model. The term continued to be used in the World Tree cosmology model but referred to a different set of planes.