Six sources of power are known to exist in the Bridgeworld.
Four of them are elemental in nature: Fire, Water, Wind and Earth.
These elements maintain the balance between the elements, inhabitants, constructs and creatures of the world. They create and destroy, they nurture and corrode, and they are the manifestation of nature within this world.
The remaining two, however, are of a very different nature: Light and Dark.
The ancient civilisations of Bridgeworld struggled to articulate the nature of Light and Darkness for one very simple reason: you could never feel them.
It was easy to feel the heat of fire, touch the flow of water, experience the caress of a breeze or walk the soil of the earth.
But Light and Dark transcended all of those things: they were visible but untouchable, and the predecessors of this realm knew there was something special.
The power of the Light was glorious in its luminescence: the power to heal, the power to create, the power to inspire hope and joy. And the legions who wielded this power rose to become the greatest commanders within the Legion ranks.
Their victories over those who wielded the powers of Darkness were hard fought, but their ultimate victory over the Dark forces in the Great Engagement led to the now-commonplace saying that no amount of Dark can ever prevail over the Light, and that it would take but a sliver of Light to pierce through any Darkness and dispell it.
Dark, so it became believed, was merely the absence of Light.
But is that so?
The Dark Power was said to be a consuming one: those who wielded it faced the risk of being consumed by an unstoppable shadow which absorbed everything around it, including the bearer of its power, including every drop of light, gradually manifesting in a darkness beyond which nothing could escape.
But what became of those Legions who embraced the Dark power?
None who have embraced the power of Darkness has ever returned to tell their tale. Their powers prior to complete consumption were said to be limitless, drawing upon everything they encountered, relentlessly consuming everything they touched or even laid their gaze upon. But all of them appeared to suffer the same fate: they simply disappeared. But nothing truly disappears. Perhaps they simply become transformed: transfigured, transposed, transmogrified.
Children's tales tell of shadows that move even in the stillness of the night, shadows that are cast by nothing at all.
Perhaps these tales aren't as far-fetched as they are made out to be.
Light and Dark are perhaps the two greatest powers in the realm, not because they are untouchable - indeed, they are. No, they are the greatest powers in the realm because they are the very existence of the realm.
It is the contrast between Light and Dark that makes things visible. For without seeing, how would one experience any Magic at all?
-- Excerpt from "Musings of a deranged summoner: the scribbles of Ralthor Khan"