The Elemental Planes are primordial realms embodying the fundamental forces from which the material order was formed. Earth, Water, Air, and Fire are not merely substances within these planes, but cosmic principles expressed without dilution. Each represents both a physical element and the deeper ideals associated with it: Earth is form, endurance, foundation, and manifestation; Water is receptivity, continuity, transformation, and the hidden depths from which possibility emerges; Air is breath, thought, freedom, motion, and the unseen passage between things; Fire is will, passion, revelation, destruction, and transformation through consuming force. Within the Mortal Plane these principles mingle together, creating matter, weather, living bodies, and the countless changing forms of the world. Within an Elemental Plane, one principle exists almost entirely unto itself.
The Elemental Planes should therefore not be understood simply as distant worlds made from enormous quantities of a particular substance. They are closer to the pure cosmic roots of those substances. Mortal stone carries something of the principle embodied by the Elemental Plane of Earth, just as every flame reflects a fragment of the force expressed without limit within the Elemental Plane of Fire. Elementals are natural expressions of these realms, beings whose existence is inseparable from the principle they embody. More complex societies have nevertheless arisen among them, and creatures such as Djinn possess identities, desires, traditions, and ambitions extending far beyond the raw element from which they originate.
Passage between the Mortal Plane and the Elemental Planes is possible through sufficiently powerful planar magic, naturally occurring breaches, and ancient gates. Such travel is exceptionally dangerous. Mortal bodies exist through a balance of the primordial elements and are poorly suited to places where one of those principles overwhelms all others. Even where the environment itself does not immediately kill an intruder, the scale and alien nature of the planes can make conventional navigation almost meaningless.
Regnum Caeli Cadentis is the Elemental Plane of Air, an endless expanse of open blue sky broken only by drifting clouds of varying density. It embodies motion, breath, thought, freedom, distance, and the invisible forces that connect one place to another. Nothing within the realm is truly still. Even its most enduring structures drift upon currents that cross distances beyond mortal reckoning, and the plane possesses neither ground nor any permanent direction that could meaningfully be called downward.
Clouds range from translucent wisps through which travelers pass unnoticed to immense stable formations capable of supporting settlements. Powerful air currents move continuously through the realm, carrying creatures, travelers, and entire cloud formations across its immeasurable reaches. These currents can become swift enough to transport something hundreds of miles before it realizes how far it has traveled, yet violent storms are comparatively rare. Regnum Caeli Cadentis is more often defined by perpetual movement than destruction.
Of the Elemental Planes, Regnum Caeli Cadentis is the most hospitable to mortal travelers, provided they possess some reliable means of sustained flight. Breathable air is abundant and temperatures across much of the plane remain survivable, though a traveler unable to remain aloft may simply fall forever. Djinn dwell throughout its boundless reaches alongside air elementals and stranger inhabitants adapted to a world without earth beneath their feet.
Regnum Magni Maris is the Elemental Plane of Water, an infinite expanse of clear turquoise sea extending without shore, seabed, or true surface. It embodies depth, continuity, receptivity, change, memory, and the capacity of one form to become another without losing its underlying nature. There is no coastline from which its waters may be observed and no final abyss awaiting those who descend far enough. Water extends endlessly in every direction.
Light permeates the realm regardless of depth, leaving even its most distant reaches illuminated by a soft aquatic radiance. Immense coral structures of extraordinary color drift freely through the endless blue, some growing large enough to resemble floating mountain ranges. Water elementals and innumerable forms of sea life gather around these reefs and along ancient currents whose courses can remain stable for centuries before slowly wandering elsewhere.
Pressure within Regnum Magni Maris can shift without warning. A region gentle enough for ordinary marine life may suddenly acquire the crushing force of an unimaginable abyss before returning to calm just as quickly. Mortal travelers must therefore possess both the ability to breathe underwater and protection against extreme changes in pressure. No natural air exists within the realm, and searching upward for a surface is futile; there is only more water.
Regnum Terrae Profundae is the Elemental Plane of Earth, an immeasurable realm formed entirely from stone, soil, crystal, metal, and mineral. It embodies foundation, permanence, structure, patience, substance, and manifestation: the principle by which possibility acquires weight, boundary, and enduring form. Unlike the open infinity of Air or Water, the infinity of Earth is enclosed. There is no horizon, only deeper strata.
Every known ore, mineral, and gemstone can be found somewhere within its depths, often in quantities impossible upon the Mortal Plane. The realm is riddled with caverns ranging from narrow fissures to chambers vast enough to swallow kingdoms. Tunnels stretch between them in immense networks created by elemental inhabitants, burrowing creatures, geological movement, and civilizations whose roads may remain intact for thousands of years before the surrounding stone closes around them.
Regnum Terrae Profundae is never entirely motionless. Frequent seismic shifts reshape its passages as colossal elemental beings move through the deep strata or immense pressures release themselves through the surrounding rock. A familiar route may become sealed beneath miles of stone while a new cavern tears itself open nearby. There is no naturally breathable air, and many enclosed spaces instead contain poisonous, corrosive, or combustible gases released from the surrounding minerals.
Among the innumerable chambers of the Elemental Plane of Earth stands Urbs Gemmarum, the City of Gems, built within a colossal crystal cavern. Its structures rise among mineral formations whose scale and purity have no equivalent in the Mortal Plane, making the city one of the few fixed landmarks known to planar travelers within an otherwise immeasurable subterranean realm.
Regnum Ignis Flagrantis is the Elemental Plane of Fire, a boundless realm composed not of earth, air, or water, but of pure flame and unbearable heat. It embodies will, passion, illumination, destruction, purification, and transformation through consuming force. Fire within the Mortal Plane requires something to burn; here, flame requires no fuel. It exists because Fire itself is one of the primordial principles upon which material existence rests.
The landscape is formed from varying densities and intensities of flame. Vast regions resemble thin seas of drifting fire, while elsewhere roaring currents become dense enough for elemental creatures to walk upon them. Towering conflagrations rise like mountain ranges, rivers of incandescent energy wind between them, and some regions burn with such intensity that heat seems almost to acquire physical substance. What appears from afar to be geography is often merely a particularly ancient or stable pattern within the greater inferno.
Elemental creatures thrive throughout Regnum Ignis Flagrantis, gathering around enduring currents and territories whose boundaries are measured through changes in heat, color, and the behavior of flame rather than stone or distance. At the heart of the realm stands Urbs Flammae Coccineae, a vast city constructed entirely from living fire, its towers and avenues maintaining recognizable shapes despite their ceaseless movement.
Regnum Ignis Flagrantis is immediately lethal to ordinary mortals. Even its least intense reaches burn hotter than natural flame, and neither mundane protection nor simple resistance to heat is sufficient for prolonged survival. Travelers require complete protection from fire before entering the plane. Without it, flesh, clothing, equipment, and eventually even resilient magical materials are consumed by the primordial force surrounding them.