The Beast Arises12 books in series
I Am Slaughter: Warhammer 40,000 Publisher's Summary
It is the 32nd millennium, and the Imperium is at peace. The Traitor Legions of Chaos are but a distant memory, and the many alien races that have long plagued mankind are held in check by the Space Marines.
When a mission to exterminate one such xenos breed on the world of Ardamantua draws in more of their forces, the Imperial Fists abandon the walls of Terra for the first time in more than a thousand years. And when another greater foe strikes, even the heroic sons of Rogal Dorn may be powerless against it. The Beast arises...and it is mighty.