Caliban

Caliban was once a world of ancient forests, mist-wreathed and beautiful and deadly, its endless woods home to great warp-touched beasts that preyed upon any who dared the wilds. To survive there was to be a warrior, and so its people organised themselves into feudal knightly orders, chivalric brotherhoods sworn to hunt the monsters and protect the scattered fortress-holds of humanity. The beasts of Caliban were no mere animals but warp-touched horrors, and to slay one was the highest honour a knight could claim.

Greatest of these was the Order, and greater still was the son of the stars who rose to lead it: the Lion, primarch of the Dark Angels. Under his command the knights waged a war of extermination against the beasts of Caliban, and by the time the Emperor arrived the world had been all but tamed, its dark forests conquered by the very brotherhood the Lion had forged.

But Caliban's story ended not in triumph but in betrayal. During the Horus Heresy, while the Lion fought among the stars, those left behind under Luther turned to darkness, and when the primarch returned he found his own homeworld arrayed against him.

The battle that followed tore Caliban apart. In the fury of the fighting the world was wracked by orbital fire and warp-fell energies until its very crust shattered, and what had been a living planet became a belt of drifting, jagged fragments. Upon the largest of these rides the Rock, the mobile fortress-monastery of the Adeptus Astartes sons who survived, forever hunting the Fallen who scattered across time and space in that terrible hour. Caliban itself is gone, but its shame endures as the darkest secret of a Chapter that has never stopped atoning.