Eye of Terror

The Eye of Terror (Ocularis Terribus in High Gothic) is a massive Warp Rift and permanent Warp Storm nearly twenty thousand light years across, a nexus of psychic energy and physical space-time where the Immaterium co-exists with realspace. It is the largest and most well-known Warp rift in the Milky Way Galaxy and is located at the rimward edge of the galaxy, to the galactic Northwest of Terra, in the Segmentum Obscurus. It is home to the largest concentration of the Forces of Chaos in realspace, including the Traitor Legions of Chaos Space Marines that fled from Terra after the end of the Horus Heresy. Incursions by Chaotic forces into the surrounding Imperial star systems are common, and the recent 13th Black Crusade launched in 999.M41 by Abaddon the Despoiler from within the Eye of Terror marked the greatest assault by the Forces of Chaos upon the Imperium of Man since the Heresy.

History
The Eye of Terror is not a naturally-occurring astronomical phenomenon. The Eye was created by the psychic shock wave that accompanied the birth of the fourth Chaos God Slaanesh, the Prince of Pleasure, during the Fall of the Eldar over 11,000 Terran years ago. The psychic shock of the birth was so great that it could not wholly be contained within the Warp, but spilled out into reality through the minds of the Eldar who died on their lost empire's homeworlds that now lie within the Eye of Terror and are known as the Crone Worlds. Consequently the Eye covers most of the region of the ancient Eldar empire. Other zones of overlap between the Warp and the physical universe were created at that time across the galaxy, but the Eye is the most significant and the largest of these Warp rifts. The Eye was originally designated a stellar anomaly known as Cygnus X-1 by the early astrographical Adepts of the Imperium of Man during the Great Crusade in the late 30th Millennium. It was Perturabo, the Primarch of the Iron Warriors Legion, who would give the Warp Rift its name as the Eye of Terror in the early days of the Horus Heresy. The existence of the Warp Rift had haunted Perturabo all his life, and his name for the anomaly was soon in use by the forces of Horus' Traitors and the Emperor of Mankind's Loyalists alike.

Ocularis Terribus
Though the reach of the Eye of Terror stretches across twenty-thousand light years of the galaxy in realspace, the region of space-time contained within the Eye constitutes its own reality, existing within both the material universe and the Empyrean dimension of the Warp. Although planets and star systems exist within the Eye, the standard physical laws of reality no longer fully apply. Time is a meaningless concept, and matter, thought and energy are indistinct and blurred with one another. The worlds within the Eye are known as Daemon Worlds and each planet constitutes its own bizarre sub-reality whose physical laws are shaped by whichever aspect of the dominant Chaos God is venerated by its inhabitants. At the very centre of the Eye lies the byssos, a hole in the fabric of reality through which raw Chaos energy pours out into the material universe. The Warp and realspace are indistinct and intermixed within the Eye, and the whole region is a maelstrom of psychic energy, impossible to navigate through normally using starships without a connection to the Dark Gods. Imperial starships avoid the area around the Eye for thousands of light years. Ships travelling too close to the Eye of Terror can be thrown far off-course - they can also be caught in temporal whirlpools which carry them backwards or forwards in time, or which trap them in temporal limbo forever. The Warp Storms that disturb the Eye are so intense that there is little point in even trying to steer a starship in a particular direction. The Chaos renegades and Chaos Space Marines who call the Eye of Terror home simply launch their starships into the swirling energies of the Warp, trusting fortune and the whims of the Ruinous Powers to carry them to their enemies. This makes Chaos attacks on the Imperium random, sudden and unpredictable, often occurring on worlds far across the galaxy from the Eye.

The Eye as a Refuge
The Eye offers a sanctuary to the worst of the Traitors and heretics forced to flee from Imperial justice. For the Traitor Legions of the Chaos Space Marines, the Eye of Terror has been their exile, sanctuary and safe haven for more than ten thousand standard years, from which they strike out at opportune, seemingly random, moments. The Eye is also a sanctuary for the most heretical renegades, fugitives of Imperial justice and traitors throughout the galaxy, and all are welcomed by the Forces of Chaos as fellow enemies of the Emperor of Mankind and the Imperium. Mortals within the Eye are constantly exposed to the effects of Chaos, becoming physically warped and mutated so their bodies come to reflect their flawed inner natures; the Chaos Space Marines of the Death Guard, for example, worship Nurgle, Chaos God of Death and Decay, so that their bodies become bloated and putrid, incubators for every form of plague and disease known in the universe.

The Cadian Gate
The Imperial world of Cadia lies nearest to the best-known stable gateway into the Eye; consequently it is the most fortified and militarized world in the Imperium, the first line of defence against Chaos incursions into realspace, thus earning the name the Cadian Gate. This area of stability is created by the network of Cadian Pylons that can be found throughout the region, instruments of Necron technology that were erected millions of years ago as part of that soulless race's great work to cut off realspace from all interaction with the Immaterium once and for all. For obvious reasons, starships exit through this gateway far more often than they enter it. The Warmaster of Chaos Undivided and leader of the Black Legion, Abaddon the Despoiler, led an attack through the Eye of Terror during a massive campaign in the 13th Black Crusade of 999.M41 that decided the fate of Cadia and many other Imperial star systems. Today, much of Cadia is currently occupied by the Forces of Chaos, but the Imperial Navy won control of the orbital space around the Cadia System and so the Chaos forces have found themselves trapped on the fortress world in a stalemate that leaves them still unable to break out into Imperial space.

Sectors and Sub-sectors surrounding the Eye of Terror
Due to the constant threat of raids and incursions, the Imperium's military forces are present in one way or another in almost every star system within 500 light years of the Eye. This military presence can range from small listening posts to heavily fortified frontier worlds.
 * Belis Corona Sector - Belis Corona is the heart of the Imperium of Man's naval efforts and its orbital spacedocks are listed in von Heffman's Glorium Imperialis as one of the wonders of the Imperium. It is said that the entirety of Battlefleet Obscurus could dock in the vast orbital shipyards in orbit above Belis Corona.
 * Medusa Sub-sector - The Medusa Sub-sector is famous as the homeworld of the Iron Hands Space Marines Chapter. Unlike many other parts of the Eye of Terror, life is hard and uncivilised barbarians inhabit many of the planets of the sub-sector.
 * Scarus Sector - Scarus Sector is the most populous of all the sectors surrounding the Eye of Terror, with no less than six Hive Worlds which come together in trade and commerce and mutual defence. There are also numerous mining and agri-worlds to support the hives. There are also two Forge Worlds, Nysa Stromolo and Mordax Prime, which supply the vast Scarus Defence Forces. It is said that 70% of the surface of Thracian Primaris, the capital world of the sector, is covered in hive cities.
 * Scelus Sector
 * Sentinel Sector
 * Belial IV - Belial IV is an Eldar Crone World that lies within the Eye of Terror.
 * Cadian Sector - The Cadian System of the Cadian Sector is possibly the most well-known star system near the Eye of Terror, with its 1st Imperial Guard Regiment having won many successful campaigns against Chaos and gaining wide recognition across the Imperium. Cadia's star system stands in the way of the only clear passage out of the Eye of Terror into the rest of Imperial space and so represents a fortress that the forces of Chaos must take if they are ever to topple the Imperium. Abaddon the Despoiler had attempted a campaign against the system almost ten thousand years ago during the First Black Crusade; after he was repelled by Imperial forces, Cadia was transformed into a fortress world against the sporadic attacks of Chaos forces in the Eye of Terror. Currently, much of Cadia remains under the control of Chaos as a result of Abaddon's 13th Black Crusade in 999.M41.
 * Chinchare Sub-sector
 * Nemesis Sub-sector
 * Caliban Sub-sector
 * Agripinaa Sector