The Nachmund Gauntlet is the only confirmed navigable passage in realspace through the Great Rift which has cut the galaxy in half since the end of the 13th Black Crusade in 999.M41. Yet the Nachmund Gauntlet brought little hope to the Imperium of easy access to the territory of the Imperium Nihilus.
The Gauntlet crossed space through the barrier of the Great Rift from the world of Vigilus in the Imperium Nihilus to the planet of Sangua Terra in the Imperium Sanctus, the half of the Imperium of Man still accessible to the light of the Astronomican.
The Cicatrix Maledictum had at least one gap, though others have been reported but not confirmed. The passage was located near the great Warp rift known as the Eye of Terror, which had been avoided by Navigators since the Great Crusade, for Warp Storms and strange anomalies have always made the region too dangerous to travel.
There, when the swirling nebula lulled, was revealed the Nachmund System. The Tyrant King of its primary planet of Dharrovar, Kaligius, ruled over the Renegade Knights of House Mandrakor who had not been seen since the Horus Heresy. Claiming Old Night had returned, Kaligius rejected all communication with the Imperium, instead forging pacts with Renegades and pirate fleets. Some Imperial starships have run the Nachmund Gauntlet successfully, but many more have been destroyed attempting the journey -- the ruined hulks of innumerable voidcraft now hang suspended in space as a vast starship graveyard.
Once considered cautious, the king's behaviour became ever more paranoid and erratic, and it was said he protected his holdings with the ferocity of an enraged drake. His defenders claimed he was like that with good reason, for on either side of the Nachmund Gauntlet was a seething tide of Chaos that constantly sought to break its metaphysical bonds and spill into realspace.
At the dawn of the Great Rift, starships that sought safe passage through the gauntlet had no choice other than to pass near Dharrovar. Those who gave the planet a wide berth were allowed to slink past without interception. Those who sought safe haven or attempted to contact the Knight World under a flag of parley were treated with hostility, suspicion or even violence.
A staunch independent, Kaligius was already convinced that no good would come from allowing the Imperium to draw him back into the fold. Instead he turned to tyranny and oppression. Even as the term Imperium Nihilus was coined, he was declared Excommunicate Traitoris.
Lord Commander of the Imperium Roboute Guilliman despatched the Castellans of the Rift, a Space Marine Chapter raised during the Ultima Founding, to drive back the hordes of daemonic war machines and Renegade Knights blighting one of the only stable routes through the Cicatrix Maledictum.
On the far side of the Nachmund Gauntlet lay the Hive World of Vigilus. Control of Vigilus allowed the Imperium to just barely keep its beleaguered worlds in the Imperium Nihilus on the far side of the rift reinforced and re-supplied; to lose it would cripple the war effort against the rampaging forces of Chaos.
Vigilus also provided a vital staging ground for the billions of refugees that come through the Nachmund Gauntlet to escape the threat of Chaos or worse in the Dark Imperium. In time, because of its strategic position, Vigilus became coveted by several of the factions of the galaxy, and the conflict known as the War of Beasts erupted on its arid surface.
- Warhammer 40,000: Rulebook (8th Edition), pg. 53
- White Dwarf (October 2017), "Eavy Metal - Create your own Chapter," pg. 118
- Wake the Dead: Lore
- Imperium Nihilus: Vigilus Defiant (8th Edition), pp. 5, 11, "To Run the Gauntlet"