"There are places that are cursed to blood and darkness and swallow all that fall into their grasp, but the paths to them may often seem fair or fortunate, thus are the unwary often led to their doom."
- —Teresa Sinos, Rogue Trader
The Jericho-Maw Warp Gate is a Warp Gate of unknown xenos origin that joins the former Imperial sector of the Jericho Reach in the Segmentum Ultima to the turbulent, Warp Storm-wracked region of space called "the Maw" half a galaxy away that divides the Calixis Sector from the Koronus Expanse in the Segmentum Obscurus.
Its origins remain utterly unexplained, and its true nature is but one of many mysteries affecting these regions.
Discovered in 755.M41 by the Imperium, the gate was active at that time, although how long this state of affairs was the case remains a matter of some debate.
Within the Ordo Xenos, many believe that the gate had been dormant for perhaps tens of Terran millennia, until some unknown cause triggered it no earlier than 397.M41, perhaps linking it to the so-called "Year of Dreaming Depths," a period of sustained and often deadly Warp disturbances affecting the Koronus Expanse.
Certainly, the gate was unknown to the people of the ancient Jericho Sector, whose once well-established Warp routes passed through its present aperture location in the past.
Warp Gates are stable two-way "conduits" between far-distant interstellar realspace locations through the Empyrean. While extraordinarily rare, they are not unknown to the Imperium, nor are they uniform in nature, appearance, or range.
Perhaps the most widespread "network" of such gates is the legendary Aeldari Webway, a series of portals interconnecting an arterial transdimensional network suspended between realspace and the Warp that once spanned the ancient domains of the Aeldari Empire, although it is now much reduced and imperiled since their fall from power.
Other Warp Gates seem to be older again in measure, far predating even the Aeldari's rise to prominence, and belonging to beings and intelligent species like the Old Ones so immeasurably ancient as to be myths of a godlike age. The Jericho-Maw Warp Gate is of this latter category, according to the Imperium's xeno-savants.
The physical structures at the two realspace termini of the Jericho-Maw Warp Gate are utterly identical: vast, irregular crescent shapes hanging silently and alone in the void of interstellar space, immobile and implacably resistant to any outside force upon them.
In appearance, they seem crafted from dark stone shot through with geometric features in tarnished golden and shadowed pearlescent metal. They shimmer slightly to the Human gaze almost as if a mirage with no more substance than a dream.
This optical illusion is further borne out by continuous and paradoxical gravitic and electromagnetic effects encountered within the gate's vicinity, and the fact that the entire structure is wrapped in a powerful dimensional shearing effect not dissimilar in nature (although many times more powerful by orders of magnitude) to an Imperial starship's Void Shields.
Any solid matter passing within the sweep of the crescent's great arms -- which span a distance over a hundred kilometres -- disappears into darkness and is hurled irresistibly to the other side of the gate and spat out, arriving on the other side of the galaxy, via what, for want of a more accurate term, might be described as a "trapdoor" in the Warp.
As far as can be discerned, the time taken by the transit is all but negligible; mere seconds of icy black dislocation spanning a distance that might take a starship under usual Warp travel a few Terran years to accomplish, if such a direct journey were even possible.
The passage is not without its perils, however, as although no Warp-Drive or Gellar Field is required to use the Warp Gate, the passage through it is a turbulent one. It was quickly discovered that any less than sturdy vessels attempting the crossing were often badly damaged or even shaken apart by the stresses of the transit, limiting the Warp Gate's practical use to warships and other strongly-constructed voidcraft.
The existence of the Jericho-Maw Warp Gate is not simply an enigma and an opportunity, but also a potential source of danger for the Imperium, which the Imperium's masters are very mindful of. The gate exists and it is open; thus, it must be dealt with if the security of the Emperor's realm is to be maintained.
The matter is complicated by the fact that the Imperium has divined no way of controlling the Warp Gate's function short of destroying the physical structure of one of its apertures; an uncertain action that would require something in the order of the firepower of an entire Imperial Navy battlefleet to accomplish.
It was this factor more than any other that made the Achilus Crusade almost inevitable, and may well precipitate drastic action should it fail.
- Deathwatch: Core Rulebook (RPG), pg. 326