Fourtheden is an Agri-World controlled by the Severan Dominate and located in the Periphery Sub-sector of the Calixis Sector. It is currently a frontline in the conflict consuming the Spinward Front. As an Agri-world, Fourtheden provides a substantial portion of the Severan Dominate's food supply. The vast majority of the Secessionists' strategic reserve came from tithes taken from this planet.
If Duke Severan XIII lost his hold on the world, several others might fall in short order. Without its bounty, the Secessionists would be unable to provide the necessary supplies to a number of worlds that rely upon imported foods. Consequently, this system and its agricultural bounty represent a key holding to the rebel forces.
Imperial forces first discovered Fourtheden during the waning days of the Angevin Crusade. By that time, High Command had already recommitted the majority of its forces to other war efforts. Expansion of the Imperium remained a primary goal, but the Crusade was considered a success, as the entire region that would eventually become the Calixis Sector was safely secured.
By this point, the exhausted forces of the extended campaign were more than adequately prepared to enjoy a well-earned rest. Even though the world appeared bountiful, its discovery came too late for the commitment that completing securing it would require. Instead, Imperial forces chose to only commit a minimal colonising effort to Fourtheden. The system was simply too far removed from more established worlds and major Warp routes for the Imperium to properly integrate it into the Calixis Sector.
Given its distance from the more civilised regions, High Command only undertook any effort at all because it was too promising of a jewel to ignore. Explorator reports strongly indicated that, with a minimal effort, a small group of colonists could establish a thriving population in relatively short order. An initial commitment of less than a million Imperial citizens soon proved this prediction true. In less than a century, much of Fourtheden’s surface was colonised, and dozens of small communities and trading centres emerged.
Ultimately, Fourtheden's early success played a key role in the development of the other worlds beyond the Periphery. Its surplus bounty provided both additional colonists and ample food supplies for nearby worlds. Without its early success, colonies on many other worlds might never have survived. This same bounty played a significant role in Duke Severus XIII's decision to secede from the Imperium. Fourtheden’s bounty of citizens and foodstuffs provide key elements necessary for the Severan Dominate to exist as an independent entity.
In spite of his dependence upon this bounty, Duke Severus XIII was readily willing to sacrifice a portion of it to help secure his stranglehold on the region. In exchange for their military support, the Duke ceded the entire population of the world's southern hemisphere to the Drukhari's Children of Thorns Kabal. By carefully limiting communications -- and blaming it on a necessary part of the war effort -- the Duke worked to isolate large portions of Fourtheden's population.
As part of his negotiations with the Drukhari, the xenos have gradually agreed to access more and more of the world. Initially, they stripped the Southern Hemisphere bare of human life -- Servitors are the only forces now undertaking agricultural work in that region. More recent reports indicate that the Children of Thorns have begun to assault communities further north. This might be a sign that negotiations have broken down, or it could be that Severus is even more desperate than previously believed.
Fourtheden enjoys a very mild climate and only slight seasonal changes. This is largely due to the fact that the world has a nearly circular orbit around its system primary, and only the slightest of axial shifts. These factors combine to yield a world with a perpetual growing season. Both the native organisms and the humans who have made it their home have adapted to take advantage of the ongoing harvests.
With little seasonal variation, surface temperatures are almost always comfortably within the ranges ideal for human life. For much of the world, rainfall is a daily event, but severe storms are exceptionally rare. Throughout the world’s recorded history, there have only been two cataclysmic storms, both of which only had a significant impact on coastal habitats and the surrounding regions. With the exception of the world’s tropical regions and its poles, Fourtheden typically has daily weather which is reminiscent of a late spring day.
The most substantial variations to the world’s climate are largely regional, due to geographic factors. For example, temperatures are far cooler near the poles and in some of the more elevated regions. In contrast, the areas nearer the planet’s equator are substantially warmer. Even in these less hospitable regions, the natives have identified useful plants that produce abundant harvests.
The system’s native life forms are almost never hostile to Terran life. In fact, the only organisms which seem capable of significantly interfering with agriculture are specimens that humans imported during Fourtheden's colonisation. It is unclear why the world's native species are so easily controlled, particularly given the world's inherent suitability for agriculture.
Some more radical agents of the Adeptus Mechanicus posited that the entire planet might be a construct, designed specifically for agricultural purposes. However, those agents were never able to accumulate any concrete evidence to corroborate such theories, and so they remain largely baseless suppositions.
- Only War: Core Rulebook (RPG), pp. 346-348
- Only War: Enemies of the Imperium (RPG), pp. 8-31