Great Wheel cosmology

The Great Wheel is the cosmology in which the world of Toril was said to exist during the first and second editions of the Advanced Dungeons & Dragons game, although the actual term "Great Wheel" didn't mean the cosmology as a whole until the 3rd edition of the D&D game and its Manual of the Planes 3rd edition. In second edition, "Great Wheel" or "Great Ring" meant the Outer Planes only. The cosmology as a whole didn't require a name other than "the Planes" or "the Multiverse," as there weren't any formally named alternatives in the AD&D game.

Ed Greenwood created the Faerûnian pantheon by choosing deities from the first edition Deities & Demigods book, sometimes renaming and modifying them, with the aim of ending up with one deity for every outer plane or outer planar layer in what we now call the Great Wheel cosmology. In this sense, the Faerûnian pantheon was created with the Great Wheel in mind.

As it was described in first and second edition, the Great Wheel was a complex, comparatively cosmopolitan place in which the gods of many worlds and pantheons mingled, the beliefs of many faiths and peoples bleeding together in a set of Outer Planes shaped predominantly by the polar forces of Law, Chaos, Good, and Evil. Thus it was that Lliira and the Greek goddess Hecate could feud over the love of the Sumerian god Enki and work at a pleasure palace operated by the Aztec gods Xochipilli and Tlazoteotl. That was in first edition, long before the debut of the Planescape setting in 1994. On Hallowed Ground noted a number of alliances between the gods of Toril and those of other worlds, for example between the original Mystra and Wee Jas of Oerth. . In the novel Tymora's Luck, a plot by a god of Toril ends up involving the gods of Krynn. .

In 3rd edition, the Forgotten Realms cosmology was retconned, with the World Tree cosmology replacing the Great Wheel. No in-game explanation was given for the change, which shifted the realms of many deities around to group them by pantheon or theme rather than alignment. Nonetheless, planes of the Great Wheel continued to receive mentions in official products. For example, in Sacrifice of the Widow, Cavatina tells that Vhaeraun's realm is in the Carceri and Eilistraee lives in Svartalfheim.

Basic Structure
While the precise details of the Great Wheel cosmology changed to various extents throughout the first, second, third, and fourth editions of the game, as described in second edition it consists of a series of somewhat concentric spheres. In the center were the Prime Material Planes (Earth-like alternative worlds) each surrounded by an Ethereal Plane (misty realms of proto-matter). Outside of the Primes and Ethereals were the inner planes, also called the elemental planes, which had their own structure based on a sphere. Then came the astral plane which connected the Prime Material Planes to each other (bypassing the Ethereal planes) and also to the last sphere, the Outer planes. The outer planes, also called the Planes of Power, were 16 planes arranged in a circle (the Great Wheel) defined mainly by alignment and surrounding a 17th neutral plane known as Concordant Opposition.

The inner planes were the six major elemental planes (Fire, Earth, Water, Air, Positive Energy, Negative Energy), the four para-elemental planes (Smoke, Ice, Ooze, Magma), and the eight quasi-elemental planes (Lightning, Steam, Radiance, Minerals, Vacuum, Salt, Ash, Dust). They can be thought of as being on the surface of a sphere with Positive Energy at the north pole, Negative Energy at the south pole and Fire, Earth, Water, and Air on the equator, equidistant from each other. The para-elemental planes are found on the equator between the boundaries of Fire, Earth, Water and Air (Magma is between Fire and Earth, for example). Four of the quasi-elemental planes are found between the boundaries of Positive Energy and the four elements (Steam is between Positive Energy and Water, for example). And the other four quasi-elemental planes are between Negative Energy and the four elements (Vacuum is between Negative Energy and Air, for example). The inner planes are surrounded by the Ethereal Planes, which also touch the Prime Material Planes and contain the various demiplanes.

Demiplanes, in second edition, are planes of finite extent found within an Ethereal Plane. They may be the creations of extremely powerful wizards, technologists, or demigods or they may be created when a large glob of proto-matter begins to pull away from its Ethereal plane and achieve separation. Demiplanes may eventually collapse in on themselves, re-merge with its parent Ethereal, or merge with an inner plane or Prime Material plane. Each demiplane has its own rules regarding gravity, vision, magic, and material make-up.

The Prime Material Plane touches both the Astral Plane and its Ethereal Plane, though these planes in the second edition cosmology do not touch one another. Though a single plane, the Prime consists of the countless crystal spheres of the Spelljammer setting, star-studded orbs that each contain a planetary system. Crystal spheres include Realmspace, which contained the Forgotten Realms setting; Greyspace, which contained the Greyhawk setting, and Krynnspace, which contained the Dragonlance setting. The spheres were surrounded by the Phlogiston, a many-colored chaos that was considered beyond the power of the gods.

Outer Planes
Many of the Outer Planes were divided into layers, infinite sub-regions that metaphysically overlap the other layers of the same plane.

Outlands
The Outlands, also called Concordant Opposition, Godsland, and simply the Land, is the plane of true Neutrality. Divine realms on this plane include the Caverns of Thought, Ilsensine's realm; the Court of Light, Shekinester's realm; Dwarven Mountain, which is the realm of Dumathoin, Vergadain, and Dugmaren Brightmantle; Annam's Hidden Realm, Semuanya's Bog, Sheela Peryroyl's Flowering Hill, Thoth's Estate, Oghma's House of Knowledge, Silvanus's realm of Summeroak, Gond's realm of Wonderhome, and Ubtao's Labyrinth of Life. The planar metropolis of Sigil is believed to be the ring seen hovering over the infinite spire in the center of the plane.

Abyss
The Abyss is the plane of Chaotic Evil.

This is the realm of Sess'innek.
 * Layer 7: The Phantom Plane

This is the realm of Umberlee and Beshaba.
 * Layer 13: Blood Tor

This is the realm of Lolth and Selvetarm.
 * Layer 66: The Demonweb Pits

This layer contains Sseth's realm, the Viper Pit, as well as the realms of Merrshaulk and Ramenos.
 * Layer 74: Smaragd

This was the realm of Kiaransalee until she was forced to flee by the return of Orcus.
 * Later 113: Thanatos

This is the realm of the troglodyte god Laogzed.
 * Layer 181: Rotting Plain

This was Moander's realm before his death.
 * Layer 223: Rarandreth

This is the realm of the bugbear deities Skiggaret and Grankhul.
 * Layer 241: Palpitatia

This is the realm of the gnome god Urdlen.
 * Layer 399: Worm Realm

This is the realm of the ogre and troll god Vaprak.
 * Layer 524: Shatterstone

Carceri
Carceri, also known as Tarterus, is located midway between Chaotic Evil and Neutral Evil. It is described as a chain of scarlet orbs stretching into infinity, the orbs of the "innner" layers nested metaphysically within the orbs of the "outer" layers like Matryoshka dolls. The Companions of the Hall visit this plane in the novel ''The Halfling's Gem.

This layer contains Talona's realm, the Palace of Poison Tears, and Grolantor's realm, the Steading.
 * Layer 2: Cathrys

This layer contains Parrafaire's realm, Trickster's Delight.
 * Layer 3: Minethys

This layer contains Vhaeraun's realm, Ellaniath, and Malar's realm, the Land of the Hunt.
 * Layer 4: Colonthys

Gray Waste
The Gray Waste, also known as Hades, is the plane of Neutral Evil.

This layer contains Kelemvor's realm, the Crystal Spire, which was formerly Myrkul's realm, the Suffering City. It also contained Urdsrest, the realm of the urd deity Kuraulyek.
 * Layer 1: Oinos

Among the roots of the world-tree Yggdrasil crawls Dendar the Night Serpent. This layer also features the Palace of Loss, Shar's realm, and Shadow Keep, the realm of Mask.
 * Layer 2: Niflheim

This layer features Rezuriel, the realm of the wicked sea-god Panzuriel.
 * Layer 3: Pluton

Gehenna
This plane is midway between Neutral Evil and Lawful Evil.

This layer features Aknuthrak, the realm of the kobold deity Gaknulak. It also featured the Throne of Blood, which was the realm of Bhaal before his death.
 * Layer 1: Khalas

This layer included the Bastion of Hate, which was Iyachtu Xvim's realm before his death. The Bastion of Hate was visited by the protagonists of Tymora's Luck. Chamada was also the site of Rictus, the realm of the dead mind flayer god Maanzecorian, and Thaotor, the realm of the cloud giant deity Memnor.
 * Layer 2: Chamada

Mungoth is the location of Death's Embrace, the realm of Velsharoon. Ondtland, the realm of Loviatar, is also on this layer.
 * Layer 3: Mungoth

The realm of the orc god Shargaas, known as the Night Below, is on this layer.
 * Layer 4: Krangath

Baator
Baator is the plane of Lawful Evil.

Tiamat's realm, the Dragonspawn Pits of Azharul, is found on this layer, as is Kurtulmak's realm Draukari and Bargrivyek's realm the Peaceable Lands.
 * Layer 1: Avernus

The sahuagin deity Sekolah lairs here in the realm of Sheyruushk. Ankhwughat, Set's realm, is also here.
 * Layer 5: Stygia

Acheron
Acheron is located between Lawful Evil and Lawful Neutral.

Avalas is the location of the orc realm of Nishrek and the goblin realm of Clangor. Bane's realm, the Black Bastion, is also on Avalas. Gilgeam's realm Zigguraxus existed here until that god's death.
 * Layer 1: Avalas

Laduguer's realm Hammergrim is here.
 * Layer 2: Thuldanin

Mechanus
Mechanus, also called Nirvana, is the plane of Lawful Neutral. It consists of only one layer. Helm's realm Everwatch, Psilofyr's realm Mycelia, Amaunator's Keep of the Eternal Sun, and Hoar's Doomcourt were all on this plane.

Arcadia
Arcadia is between Lawful Neutral and Lawful Good.

Mount Clangeddin, home of the dwarf god Clangeddin Silverbeard, is located here.
 * Layer 1: Abellio

Buxenus is the home of Azuth's realm, Azuth, and Heliopolis, the largest realm of the Mulhorandi pantheon.
 * Layer 2: Buxenus

Mount Celestia
Mount Celestia, also known as the Seven Heavens, is the plane of Lawful Good.

Tyr's realm, the Court, is located here.
 * Layer 1: Lunia

Bahamut's realm, Bahamut's Palace, is found here and the other first four layers of the plane.
 * Layer 2: Mercuria

The Green Fields, home of the halfling pantheon, is here.
 * Layer 3: Venya


 * Layer 4: Solonia

Erackinor is the realm of Moradin and Berronar Truesilver. Uroborus is the realm of Jazirian.

Bytopia
Bytopia, also called the Twin Paradises, is between Lawful Good and Neutral Good.

The Golden Hills, home of the gnome pantheon, is located here.
 * Layer 1: Dothion

Martyrdomain, realm of Ilmater, is located here.
 * Layer 2: Shurrock

Elysium
Elysium is the plane of Neutral Good.

The City of the Star is the realm of Isis, although she also dwells in Heliopolis on Arcadia.
 * Layer 1: Amoria

Morninglory is the realm of Lathander. Woodhaven is the realm of the giant goddess Hiatea. The Great Mother's Garden is the realm of Chauntea. Dweomerheart was the realm of Mystra; it was located in Mechanus before the death of the original Mystra during the Time of Troubles. Eldath's realm, the True Grove, is also on this layer.
 * Layer 2: Amoria

Selkie's Grotto is the realm of Surminare.
 * Layer 4: Thalasia

Beastlands
Also called the Happy Hunting Grounds, the Beastlands are between Neutral Good and Chaotic Good.

The Forbidden Plateau is Ubtao's realm. Shiallia's realm is the High Grove. Nobanion's realm is the Pridelands. Skerrit's Glade is the realm of Skerrit. The Grove of the Unicorns is the realm of Mielikki.
 * Layer 1: Krigala

The Library of All Knowledge is the realm of Deneir and Milil.
 * Layer 2: Brux

Stormhold is the realm of Stronmaus.
 * Layer 3: Karasuthra

Arborea
Also called Olympus and Arvandor, Arborea is the plane of Chaotic Good.

Arvandor, which the elves use as the name of both the layer and plane, is the home of the Seldarine. Brightwater is the realm of Lliira, Sharess, Sune, and Tymora.
 * Layer 1: Arvandor

Elavandor is the realm of Deep Sashelas.
 * Layer 2: Aquallor

Amun-Thys is the realm of Nephthys.
 * Layer 3: Mithardir

Ysgard
Ysgard, also called Gladsheim, is between Chaotic Good and Chaotic Neutral. Selune dwells in the Gates of the Moon. Sharess dwells in Merretet in her aspect as Bast. Jotunheim is the realm of Surtr and Thrym. Shaunidaur is the realm of Shaundakul. Netaph is the realm of Anhur. Safe Harbor is the realm of Valkur. Uthgardheim is the realm of Uthgar.
 * Layer 1: Ysgard

Muspelheim is the realm of Surtr.
 * Layer 2: Muspelheim

Nidavellir is the realm of Marthammor Duin. Svartalfheim is the realm of Eilistraee.
 * Layer 3: Nidavellir

Limbo
Limbo is the plane of Chaotic Neutral. Whether or not it has layers is the subject of some disagreement.

Fennimar is the realm of Fenmarel Mestarine. Knight's Rest is the realm of Tempus.

Pandemonium
Pandemonium is between Chaotic Neutral and Chaotic Evil.

The Towers of Ruin are the realm of Talos. Auril dwells in Winter's Hall.
 * Layer 1: Pandesmos

Hruggekolohk is Hruggek's realm. The Shattered Castle (also known as the Supreme Throne) is the realm of Cyric. Battle Guarde is the realm of Garagos.
 * Layer 2: Cocytus

Hidden Betrayal is the realm of the derro god Diirinka. The Unseelie Court is the realm of the Queen of Air and Darkness.
 * Layer 3: Phlegethon

Air
The Great Funnel is Akadi's realm.

Earth
The Great Mountain is the realm of Grumbar. The Cavern Under the Stars is the realm of Geb.

Fire
The Crimson Pillar is the realm of Kossuth.

Ooze
The Paraelemental Plane of Ooze, located between the planes of Earth and Water, is the home of Ghaunadaur's realm, the Cauldron of Slime.

Water
Sea of Timelessness is the realm of Istishia. The Murky Depths is the realm of Blibdoolpoolp. Shelluria is the realm of Eadro and Persana.