Great Wheel

The Great Wheel is a term from Dungeons & Dragons that came into being with the AD&D setting Planescape. It refers to the structure of the multiverse, as D&D ultimately arranged its cosmology in a pattern resembling a set of consecutive rings or circles; the Prime Material Plane at the center, bordered by the Ethereal Plane, and then by the Elemental Planes, which are bordered in turn by the Astral Plane - these together make up the "Inner Planes". After that comes the assorted Character alignment-based "Outer" Planes, divided into the Good-based Upper Planes, the Neutral-based Middle Planes, and the Evil-based Lower Planes.

It is the most iconic cosmological set-up and is generally upheld as definitive for D&D as a whole, even if some settings like Dragonlance and Eberron break away from the mold. In 4th edition, the Great Wheel was replaced by the World Axis cosmology, and even though instructions on how to reshape the latter into the former were provided, it was the source of much uproar.

The Great Wheel is intimately tied up with the Blood War.