Magog is a verdant Fortress World found in the Jericho Reach, mutated by continuous contact with the Warp energies emanating from the Hadex Anomaly, making it a prime recruiting ground for the Stigmartus Chaos Cult.
The Magog System has been drawn into and exited from the Hadex Anomaly countless times in the millennia since the disturbance first appeared. These transitions have had a substantial effect upon its only inhabitable planet and those who dwell upon it.
Once this was a stable Agri-world filled with citizens loyal to the God-Emperor and the Imperial Creed. Now, it is a breeding ground and a training centre for the forces of corruption that extend into the Jericho Reach.
The planet's environment and indigenous life all bear the taint of the Warp. Rivers that were once filled with water now flow with blood. Much of the plant life -- including some that is harvested for food -- is predatory and feeds upon those who tend it.
The planet's surface ebbs and flows, as though the entire world draws breath. Landmasses -- even mountain ranges -- migrate on a whim and are often subsumed beneath the world's surface, only to emerge solar days or decades later in a different locale.
In addition to those surviving Humans, the planet is also rife with creatures spawned from the Warp. These foul daemons closely interact with the tainted Humans; breeding mutants and providing a seemingly endless supply of further soldiers for the forces of the Dark Gods.
Their presence serves as a powerful motivation for the tainted Humans as they pay their obeisance. The mortals are constantly driven to commit acts of debauchery and cruelty in their service.
In spite of these constant acts of wanton destruction, Magog remains a crucial asset to the forces of Chaos. For unknown reasons, the planet's environment has consistently remained capable of supporting life and abundant agriculture.
Though the foodstuffs are hideously deformed, the dark Fortress World's fields are constantly tilled and harvested by countless slaves. The mutated crops provide yields with an efficiency that far exceeds even many of the most bountiful planets of the Imperium.
This bounty of both food and manpower is likely the reason for the system's extensive defences, and very few of the voidcraft sent to scout the system have returned from their missions. While Warp instability contributes to the high failure rate, the dark fleets reported by those that have returned are undoubtedly a factor as well.
Reports have also indicated that there are substantial orbital emplacements, one of which has been tentatively identified as a Blackstone Fortress.
The Stigmartus cult actively recruits from Magog's population. There are numerous reports of Traitor Marines active in the Magog System, or moving towards the system. The extent of their involvement is unclear, but they may be recruiting new Heretic Astartes from the native population as well.
Magog's many uses clearly dictate that it must be a high priority target for the Achilus Crusade to retake the Jericho Reach. However, until additional assets can be allocated it is virtually impenetrable. The Chaos forces must be drawn away from the system, or the Acheros Salient would need to receive a substantial increase in manpower and resources.
- Deathwatch: The Achilus Assault (RPG), pg. 76