Pelion, or Mithardir ("white dust") by the Seldarine, is the third and lowest layer of Arborea. In vast contrast to the vibrant lands of Olympus and Ossa, Pelion is nothing more than an endless desert of pure white sand, dotted with ancient ruins dating back to the earliest days of the planes. Travelers beware in Pelion just as much as above, though, for this desert is cruel and unyielding. This land is not merely subject to the normal risks of desert landscapes, of heat and dehydration, for despite the emptiness, the weather here can be just as vicious as the rest of the plane; here, the huge, sudden thunderstorms known across Arborea strike same as they do above. Of course, here they bring not just lighting and rain, but tremendous dust storms driven in front of them, enough to easily bury an unsuspecting berk before they can blink.
According to some sages, Pelion — being an endless, empty realm of nothing but ancient ruins filled with long-lost treasures, traps, and ancient defenders — is the physical manifestation of the Dungeon archetype, by far the most common facet of quest structures upon the Prime, though less so on the planes. Whatever the place it serves in Arborea, though, it is treasured by historians across the multiverse as the sole remnants of the first multiversal civilizations, the ruins preserved far more than they are anywhere else, seemingly immune to the shifting core natures of mortal thought that have wiped out nearly all evidence of these first civilizations from the other Outer Planes.
But for Amun-thys, the realm of the goddess Nephythys, Pelion is entirely without civilization, with no settlements, no colonies, no natives. Nothing more complex than simple desert flora and fauna lives in Pelion, and any attempts at building here are doomed to failure. The desert seems to hate all encroachment, and it isn't long before any construction on Pelion is buried beneath the shifting sands. However, both the Olympians and the Seldarine have legends of the ancient past of Pelion.
According to the Olympians, Pelion was long ago the realm of the Ennead, in the days when Ptah led the pantheon. As his worship declined, though, his realm shrank, taken by the white sands. The pantheon dispersed across the planes, and Ra took control, while Ptah just managed to cling to divinity. The followers of the Ennead are fairly mum on the issue, saying nothing either way as to the accuracy of this tale.
The Seldarine, however, have a different story regarding Pelion's ancient past. As they tell it, the Animal Lords of the Beastlands once took Pelion as their home. But as the most important parts of their realms drifted to the Beastlands, the Animal Lords went with them, until there was nothing left but the sand. Again, the Animal Lords themselves seem not to care enough to bother clearing up the issue.
Whichever is true, if either, or perhaps even both, nowadays Pelion is nothing but a place where adventurers can seek out the ancient relics and treasures of days gone by.
- Manual of the Planes, pg.146
- Planes of Chaos - Book of Chaos, pg.54