Acheron was the bridge between the ultimate order of Nirvana and the regimented evil of the Nine Hells and as such, each layer emphasized order over evil. The land masses on each layer were blocks of geometric simplicity the size of nations floating in a sea of air. The blocks would slowly collide and part without causing any upheaval or tremor, allowing beings to move to a new block if desired. The dance of the blocks was carefully orchestrated and creatures of high intelligence could usually discern a pattern for an area by studying the motions. It was said gravity pulled toward the center of the blocks but in practical terms gravity was normal to each surface.
Acheron was sometimes known as the "iron-shod battle planes of Acheron" due to the characteristics of the first layer, Avalas. The blocks of the top plane were black with a metallic hardness that allowed the sounds of battle and troop movements to reverberate loudly. Avalas had the most block-like worlds and the highest population as the armies of the Outer Planes spent their afterlife clashing in neutral territory over differences both subtle and gross. The landscape consisted of cone-shaped mountains and pits plus the iron fortresses of the various armies. The only other remarkable feature of this layer was the river Styx that would bubble up from one pit, meander across two or three sides of a block, and then disappear down another pit. The Styx did not visit all the blocks, but those it did could be reached by Charon and his servants.
Avalas touched the Astral Plane and had spherical portals to the three adjacent planes: Nirvana, the Nine Hells, and Concordant Opposition. The portals hung at fixed locations in space and would pass harmlessly through the blocks, becoming inactive while inside a block and reactivating when they reappeared. Anyone emerging from a portal would start to fall toward the nearest block and almost certainly required some form of flight to avoid a high velocity impact. The portals were activated by touch and the destination could be determined by the sound it made when activated. A harmonious chord indicated a portal to Nirvana, a dissonant chord meant the Nine Hells, and silence indicated Concordant Opposition.
Avalas was the location of the orc realm of Nishrek and the goblin realm of Clangor. Bane's realm, the Black Bastion, was also on Avalas. Gilgeam's realm Zigguraxus existed here until that god's death.
This layer was the Sargasso Sea, Elephants' graveyard, and scrap heap for countless contraptions, creations, weapons, armor, failed experiments, broken devices, fallen buildings, and shipwrecks of sea and air. The blocks of Thuldanin were hollow and pockmarked with pits that lead to the interior a few miles/kilometers down. There the flotsam and jetsam of the ages turned to stone in a matter of days or weeks due to the magic of this layer. Thuldanin had no inhabitants, only the occasional visitor from Avalas looking for some piece of magic or technology that might turn the tide of battle.
The third layer of Acheron had blocks different than those of the other layers. Here the blocks were made of gray volcanic stone and the faces were six-sided, eight-sided, or even higher in number of edges. When the blocks of Tintibulus collided the surfaces would fracture along natural fault lines into hexagons great and small. This layer had no inhabitants but was attractive to magical researchers for its emptiness and isolation.
The blocks of the fourth and final layer were square and so razor-thin as to be almost two-dimensional. They ranged in size from a few inches/centimeters to several miles/kilometers across. Both sides of the hard black squares had normal gravity pulling to the surface and could be walked upon. Being hit by the edge of one of these razor-sharp squares could be deadly.
The main inhabitants of Acheron were the spirit legions occupying Avalas. They were made up of the spirits of humans, dwarves, halflings, ogres, and many other mindless soldiers who died in wars after forgetting their purpose; those for whom war became an end in itself. The spirits would congregate with others of similar beliefs or alignment and form nations on the surface of a block. They would fight to control a block and then join forces to conquer another block when it came within their reach. Legion members who were slain in battle would return with full strength within 24 hours, ready to fight again. The orc and goblinoid spirit legions shared the same large block in Avalas and besieged one another regularly.
- Bahgtru, son of Gruumsh, held a realm on a smaller block which orbited Gruumsh's block.
- Bane, God of Strife, Hatred, and Tyranny, once had a realm in Acheron before he was slain by Torm during the Time of Troubles. After his resurrection, he carved out a realm in the Barrens of Doom and Despair as described by the World Tree cosmology model. (After the Spellplague he had his own realm, Banehold, that floated in the Astral Sea as described by the World Axis cosmology model.)
- Deep Duerra maintained the Citadel of Thought in Thuldanin.
- Gilgeam, Supreme Ruler of Unther, had his realm, Zigguraxus, on Avalas.
- Gruumsh of the orcs at one time made his home, Nishrek, consisting of several large citadels, on a large block in the first layer.
- Ilneval, lieutenant of Gruumsh, had holdings on a smaller block which orbited Gruumsh's block.
- Khurgorbaeyag, goblin god of slavery and patron of the Batiri, resided in his pantheon's realm of Clangor in Avalas.
- Laduguer, the Gray Protector of the duergar, maintained his realm of Hammergrim on Thuldanin.
- Luthic, the cave goddess and wife of Gruumsh, lived on a smaller block that orbited Gruumsh's block.
- Maglubiyet, war god of the goblins and hobgoblins, shared the same block as Gruumsh and maintained citadels as well in the never-ending battle between these hated enemies. His realm was named Clangor.
- Nomog-Geaya, the divine General of the hobgoblins, resided with his superior in Clangor.
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 Jeff Grubb (July 1987). Manual of the Planes 1st edition. (TSR), p. 113. ISBN 0880383992.
- ↑ 2.0 2.1 Jeff Grubb, Bruce R. Cordell, David Noonan (September 2001). Manual of the Planes 3rd edition. (Wizards of the Coast), pp. 123–127. ISBN 0-7869-1850-8.
- ↑ Jeff Grubb (April 1987). “Plane Speaking: Tuning in to the Outer Planes”. In Roger E. Moore ed. Dragon #120 (TSR, Inc.), pp. 42–43.
- ↑ 4.0 4.1 Jeff Grubb (July 1987). Manual of the Planes 1st edition. (TSR), p. 73. ISBN 0880383992.
- ↑ Jeff Grubb (July 1987). Manual of the Planes 1st edition. (TSR), pp. 78–82. ISBN 0880383992.
- ↑ Mike Mearls, Jeremy Crawford, Christopher Perkins, James Wyatt (2014). Dungeon Master's Guide 5th edition. (Wizards of the Coast), p. 58. ISBN 978-0786965622.
- ↑ Frank Mentzer (January 1985). “Ay pronunseeAYshun gyd”. In Kim Mohan ed. Dragon #93 (TSR, Inc.), p. 25.
- ↑ Richard Baker, James Wyatt (March 2004). Player's Guide to Faerûn. (Wizards of the Coast), p. 147. ISBN 0-7869-3134-5.
- ↑ Richard Baker, James Wyatt (March 2004). Player's Guide to Faerûn. (Wizards of the Coast), p. 161. ISBN 0-7869-3134-5.
- ↑ Richard Baker, James Wyatt (March 2004). Player's Guide to Faerûn. (Wizards of the Coast), p. 163. ISBN 0-7869-3134-5.
- ↑ Bruce R. Cordell, Ed Greenwood, Chris Sims (August 2008). Forgotten Realms Campaign Guide. (Wizards of the Coast), pp. 64, 65. ISBN 978-0-7869-4924-3.
- ↑ 12.0 12.1 Eric L. Boyd (1997). Powers and Pantheons. (TSR, Inc), p. 102. ISBN 0-7869-0657-X.
- ↑ 13.0 13.1 13.2 13.3 13.4 13.5 Jeff Grubb (July 1987). Manual of the Planes 1st edition. (TSR), p. 114. ISBN 0880383992.
- ↑ Jeff Grubb, Ed Greenwood and Karen S. Martin (1987). Forgotten Realms Campaign Set (Cyclopedia of the Realms). (TSR, Inc), p. 10. ISBN 0-8803-8472-7.
- ↑ Jeff Grubb and Ed Greenwood (1990). Forgotten Realms Adventures. (TSR, Inc), p. 37. ISBN 0-8803-8828-5.
- ↑ Ed Greenwood, Sean K. Reynolds, Skip Williams, Rob Heinsoo (June 2001). Forgotten Realms Campaign Setting 3rd edition. (Wizards of the Coast), p. 238. ISBN 0-7869-1836-5.
- ↑ Richard Baker, James Wyatt (March 2004). Player's Guide to Faerûn. (Wizards of the Coast), p. 145. ISBN 0-7869-3134-5.
- ↑ Bruce R. Cordell, Ed Greenwood, Chris Sims (August 2008). Forgotten Realms Campaign Guide. (Wizards of the Coast), p. 62. ISBN 978-0-7869-4924-3.
- ↑ Eric L. Boyd (1998). Demihuman Deities. (Wizards of the Coast), p. 62. ISBN 0-7869-1239-1.
- ↑ Colin McComb (1996). On Hallowed Ground. Edited by Ray Vallese. (TSR, Inc), p. 133. ISBN 0-7869-0430-5.
- ↑ Eric L. Boyd (1998). Demihuman Deities. (Wizards of the Coast), p. 85. ISBN 0-7869-1239-1.
- ↑ 22.0 22.1 22.2 Colin McComb (1996). On Hallowed Ground. Edited by Ray Vallese. (TSR, Inc), p. 132. ISBN 0-7869-0430-5.
- ↑ Eric L. Boyd (1998). Demihuman Deities. (Wizards of the Coast), p. 71. ISBN 0-7869-1239-1.
Prime Material plane • Feywild • Shadowfell
Transitive Planes: Astral Plane • Ethereal plane
Inner Planes: Elemental Plane of Air • Elemental Plane of Water • Elemental Plane of Earth • Elemental Plane of Fire • Elemental Chaos
Para-Elemental Planes: Frostfell • Swamp of Oblivion • Fountains of Creation • Great Conflagration
Quasi-Elemental Planes: Lightning • Radiance • Minerals • Steam • Vacuum • Ash • Dust • Salt
Outer Planes: Arcadia • Mount Celestia • Bytopia • Elysium • Beastlands • Arborea • Ysgard • Limbo •
Pandemonium • Abyss (Layers) • Carceri • Hades • Gehenna • Nine Hells • Acheron • Mechanus
Energy planes: Positive Energy plane • Negative Energy plane
Prime Material plane • Cynosure • Fugue Plane
Transitive Planes: Astral Plane • Ethereal plane • Plane of Shadow
Celestial Outer Planes: Arvandor • Brightwater • Dwarfhome • Dweomerheart • Gates of the Moon • Golden Hills • Green Fields • House of Knowledge • House of the Triad
Fiendish Outer Planes: Abyss (Layers) • Barrens of Doom and Despair • Blood Rift • Clangor • Deep Caverns • Demonweb Pits • Fated Depths • Fury's Heart • Hammergrim • Nine Hells • Nishrek • Supreme Throne
Neutral Outer Planes: Dragon Eyrie • Heliopolis • House of Nature • Jotunheim • Warrior's Rest
Inner Planes: Elemental Plane of Air • Elemental Plane of Earth • Elemental Plane of Fire • Elemental Plane of Water • Positive Energy plane • Negative Energy plane
Prime Material plane
Fundamental planes: Astral Sea • Elemental Chaos
Astral dominions: Arvandor • Banehold • Celestia • Cynosure • Deep Wilds • Demonweb Pits • Dismal Caverns • Dwarfhome • Eternal Sun • Fugue Plane • Gates of the Moon • Green Fields • House of Knowledge • Nine Hells • Nishrek • Supreme Throne • Towers of Night • Tu'narath • Warrior's Rest
Elemental realms: Abyss (Layers) • City of Brass • Cresting Spires • Fimbulwinter • Hidden Realm • Muspelheim • Root Hold • Sky Home • Steading • Thraotor • Undying Pyre • Zerthadlun
Parallel planes: Feywild • Shadowfell
Anomalous planes: Far Realm