Endurance Explored Part One (WIP)

Endurance, last hope of the Raven Guard, sits darkly in space. A strange world on the fringe of the galaxy.  From space it appears dead, like a scarred mass of stone.  Tall, jagged mountains pierce the surface like ancient blades of obsidian, deep craggy canyons like flesh torn by wild animals.  Moss and lichen cover anywhere that sees even the slightest light.  Yet it is not on the surface that its inhabitants live, but in great underground caverns and on the steep canyon walls.  Huge monolithic stalagtites stand guard to the entrances of these great cities.  The entrances giving not even the slightest clue as to the civilization that lives inside.  The dank air outside smells earthy like fresh soil, yet the air within the caverns smells sterile and stale.   Upon closer inspection one might notice the exhaust vents from great manufactorum or the faint glow of lights within the canyons.  These hidden cities, interlinked by great tunnel highways, are thriving industrial metropolis's.  One would struggle to navigate the roadways as they're designed to confuse intruders thus few ever travel from one city to the next. 
The Endurians had now been there thousands of years, they have withstood invasions of great monstrous daemon hordes and the fierce Dark Eldar.  Every group on the planet contributes to the defense: the Space Marines fleet is ever ready to engage enemy vessels and the legionaries stand guard from their fortress known simply as ; the people volunteer regularly for the Planetary Defense Force (PDF) and work the manufactorum to build weapons, armor, vehicles, and ships even; and the Mechanicum deploys the small titan legion, Legio Corviticus, when circumstances require and run the industrial sectors to produce everything an army could need.