Actum Celandi

Summary

The Actum Celandi is also known as the Act of Concealment. It happened after the war between the Gods and Mankind. It is believed that after the war the Gods decided that being on the material plane was too dangerous, out of fear of the Titans being ever released from Tartarus, also known as Carceri. Because of this the Gods decided to cut off the inner planes from the rest of the planes, creating a sort of bubble or net around it. This meant that even though the Gods presence and their magic were still alive in the inner planes and could be tapped into, the Gods themselves couldn't walk the material plane anymore. They can still help people and perform minor miracles here and there, and they are still able to collect the souls of the deceased.
Together inside of the bubble, or net, that has been cast by the Gods one can find the Ethereal Plane, the Feywild, the Material Plane, the Shadowfell and the Elemental Planes of Fire, Water, Earth and Air. This is because both the Feywild and the Shadowfell inhabit nearly the same place as the Material Plane, but slightly out of faze, and the elemental planes is what the Inner Planes are made out of. The Elemental Chaos and Ethereal Plane form an extra barrier protecting the Material Plane, the Feywild and the Shadowfell. This also means that travel between the Feywild, Material Plane, Shadowfell, Ethereal Plane and the Elemental Planes is much easier and can be done by opening portals. However going from any of these eight places to any of the outer planes or negative planes is near impossible, this is what the Act of Concealment was, to cut off the inner planes from the outer planes as much as possible, without upsetting the balance of the universe.

Historical Basis

The myth is rooted in an actual historical event that is known as the Act of Concealment. Stories and pieces of art from before the Act of Concealment have all been lost, but some painting and statues have been found that are believed to be from just after the Act of Concealment that show what scholars and historian believe to be real. A place where Mankind and the Gods walked together on the material plane.

Spread

This legend is common knowledge, though some scholars and historians who have dedicated their lives to finding and storing information might be able to tell you more in depth information about the Outer Planes and what resides in them.

In Literature

The actual representation of how the Cosmos looks like is different for the pantheons. Widely accepted is the Great Wheel, which is depicted above, but some pantheons see it as the tree Yggdrasil. The basis of it though all say the same things, with some planes having a different name.