The Arch

The worlds, planes, and the magical Weave that flows between them all is called the Arch.

The World Axis

Since time immemorial, the Arch was arranged as an axis. The Prime was at the center, with the Fundamental Planes and the Parallel Planes rotating around it.

The Great Wheel

After the Starfire Calamity , there was a great shattering of the Arch. Planes were ripped from reality and thrown into the nothingness of space-time. The gods were helpless to save it - the end was here. Yet, something happened. The Arch rearranged itself. The cosmology warped and changed until the Great Wheel was born.
The Prime was the nexus. It was the beating heart at the elemental and philosophical center of this new Great Wheel. The Echoes, Inner Planes, and Outer Planes all formed from the remains of the World Axis - with Sigil remaining the central node of travel in the multiverse.

The World Axis

The Great Wheel