Cosmology of Eberron

Eberron is part of the Great Wheel of the multiverse, as described in the Player’s Handbook and the Dungeon Master’s Guide. At the same time, it is fundamentally apart from the rest of the Great Wheel, sealed off from the other planes even while it’s encircled by its own wheeling cosmology. Eberron’s unique station in the multiverse is an important aspect of the world: its planes have profound and shifting influences on the Material Plane, and it is sheltered from the influences and machinations of gods and other powers elsewhere on the Great Wheel.
The planet of Eberron is the heart of its own Material Plane. It is surrounded by the Ring of Siberys. Beyond this band of dragonshards, twelve moons orbit the world. To date, no creature from Eberron has explored the moons, and none can say whether they are lifeless rocks or thriving worlds. Some sages believe that the moons are connected to the planes, or that they might even be physical extensions of the planes, but the truth of these assertions remains unknown.
No other planets have been discovered within Eberron’s Material Plane. The underworld of Khyber, however, contains a host of demiplanes, tiny pockets of altered reality. As such, venturing beneath the surface of Eberron can lead you to a network of caverns and passages, and if you find the right passage, it can take you to fantastic and deadly places inhabited by fiends, aberrations, and other children of Khyber.
Tour of the Planes
Daanvi, the Perfect Order
Dal Quor, the Region of Dreams
Dolurrh, the Realm of the Dead
Fernia, the Sea of Fire
Irian, the Eternal Dawn
Kythri, the Churning Chaos
Lamannia, the Twilight Forest
Mabar, the Endless Night
Risia, the Plain of Ice
Shavarath, the Battleground
Syrania, the Azure Sky
Thelanis, the Faerie Court
Xoriat, the Realm of Madness

The Material Plane is enfolded by thirteen planes of existence. Many of these have aspects of both Outer Planes and Inner Planes. All of them overlap with Eberron in some way, and they influence and are influenced by the Material Plane. The intensity of this influence waxes and wanes; scholars often depict the planes as orbiting Eberron—sometimes coming close, other times far away—though this manner of expression is merely a metaphor for their shifting influence. When another plane’s influence on the Material Plane is especially strong, the plane is said to be coterminous. When its influence is weak, a plane is remote. The state of a plane can be important for performing epic rituals, creating of eldritch machines, or interacting with extraplanar entities. Whether or not a plane is remote or coterminous at a given time depends entirely on the needs of your story.

Manifest Zones
At certain places in the Material Plane, the barriers between worlds are thin, and some characteristics of another plane can bleed through into the material world. These places are called manifest zones, and the nature of each one is strongly shaped by the plane it connects to. The city of Sharn is located in a manifest zone linked to Syrania that keeps its towers reaching toward the sky and aids flight. Ghosts might linger in a manifest zone associated with Dolurrh, while a manifest zone tied to Lamannia might have wild vegetation and enhance druidic magic. A manifest zone might include a portal that allows free passage from either plane to the other. The descriptions of other planes in this section offer some other possible effects. Most manifest zones have reliable, persistent effects. Some have only weak connections to their planes, and their properties influence the world only when the plane is coterminous.

Type

Study, Scientific

Eberron and the Multiverse
It is theoretically possible to travel between Eberron and other worlds in the multiverse by means of the Deep Ethereal or various spells designed for planar travel, but the cosmology of Eberron is specifically designed to prevent such travel, to keep the world hidden away from the meddling of gods, celestials, and fiends from beyond.
The three progenitor wyrms worked together to form Eberron and its planes as a new cosmic system in the depths of the Ethereal Plane. They recreated the elves, orcs, dragons, and other races found throughout the multiverse and placed them in their new world, but allowed them to develop beyond the reach of Gruumsh, Corellon, Lolth, and other influences for good and ill.
In your campaign, you might decide that the barrier formed by the Ring of Siberys is intact, and contact between Eberron and the worlds and planes beyond its cosmology is impossible. This is the default assumption of this book. On the other hand, you might want to incorporate elements from other realms. Perhaps you want to use a published adventure that involves Tiamat or the forces of the Abyss meddling in the affairs of the world. In such a case, it could be that the protection offered by the Ring of Siberys has begun to fail. You might link the weakening of Siberys to the Mourning—perhaps whatever magical catastrophe caused the Mourning also disrupted the Ring of Siberys, or perhaps a disruption of the Ring of Siberys actually caused the Mourning!
If contact between Eberron and the wider multiverse is recent and limited, consider the implications for everyone involved. In the Great Wheel, Asmodeus is an ancient threat, with well-established cults, lines of tieflings, and a long history of meddling that sages might uncover in dusty old tomes hidden in remote libraries. But if Asmodeus has only just discovered Eberron and begun to influence it for the first time, there is no lore about him to be discovered on Eberron. He has no power base and needs to recruit new followers. Unusual alliances might form against him, as celestials and fiends join forces to expel this hostile outsider.