Following the Traitor victory at the Drop Site Massacre on Istvaan V, the Warmaster Horus Lupercal despatched the homicidal Primarch Konrad Curze and his psychotic VIIIth Legion, the Night Lords, on a campaign of genocide against the Imperial strongholds of Heroldar and Thramas in the Aegis Sub-sector of the Thramas Sector in the Eastern Fringes.
The campaign was intended to protect Horus' flank and supply lines as he prepared for his main drive on Terra from Istvaan V and delay the Dark Angels Legion from reinforcing the Loyalist defence of the Throneworld.
This bitterly contested campaign would drag on for nearly three Terran years and succeed at carrying out Horus' objective, though at terrible cost to the Night Lords.
Following the victory of the Drop Site Massacre at Istvaan V, Horus called a meeting of the 8 Primarchs of the Traitor Legions, with only the the Alpha Legion's Primarch Alpharius missing, aboard his flagship, the Vengeful Spirit.
Five of the Primarchs met in person, including Horus, Fulgrim, Angron, Mortarion, and Lorgar. Three appeared through the use of hololithic emitters that transmitted their signals through the Warp, including Perturabo, Konrad Curze and Magnus the Red, who had only recently joined the Traitors after the Burning of Prospero, when the broken remains of his Thousand Sons had been transported by Tzeentch into the Eye of Terror to the Planet of the Sorcerers. The conclave of Traitor Primarchs made ready their plans for the next step in their war against the Emperor. With the meeting complete each Legion went its way according to its assigned role.
The Night Haunter's fleet, augmented by the entirety of the Legio Ulricon, a Traitor Titan Legion, had already departed, bound for the planet of Tsagualsa, a remote world in the Eastern Fringe that lay shrouded in the shadow of a great asteroid belt. From there, the Night Lords' terror troops would begin a campaign of genocide against the Imperial strongholds of Heroldar and Thramas, star systems that, if not taken, would leave the flanks of the Warmaster's strike on Terra vulnerable to attack by the Loyalists.
The Thramas System was of particular importance, as it comprised a number of Mechanicum Forge Worlds whose loyalty still belonged to the Emperor. Before Horus' treachery had been revealed at Istvaan III he had ordered the Primarch Lion El'Jonson and the bulk of his Dark Angels Legion to the Eastern Fringe, there to unwittingly perish at the murderous hands of their treacherous kin.
Following two Terran years of bitter fighting, and extensive losses on both sides, the Lion could barely scarce to give it countenance. In an attempt to sway his brother Lion El'Jonson to Horus' cause, the Night Haunter had left a deep-void beacon in the patrol path of one of the Dark Angels' outrider vessels. The beacon was set to transmit coordinates in advance, so that the two Primarchs could meet and parley on the planet of Tsagualsa.
Night Haunter wanted to break his former brother either mentally, physically or both to obtain his objectives. The Primarchs were escorted by two warriors from their personal Honour Guards to the parley. Lion El' Jonson was accompanied by Paladin Corswain of the 9th Order and Master Alajos, while Konrad Curze was flanked by First Captain Jago Sevatarion and his Equerry, Captain Sheng.
The meeting began amicably enough between the two as they conversed with relative civility. This lasted only until the Night Haunter slandered the Lion, and in return El'Jonson struck his brother. This melee further degenerated into an all-out brawl between the two sides. Kurze managed to gain the upper hand and began to strangle the life out of El'Jonson. Fortunately, Corswain ran his sword through the Night Haunter's back, thus saving his Primarch's life and rendering Kurze comatose. Eventually both Legions sent reinforcements in response to the incident. Each side dragged away their respective Primarchs from the scene of the combat. Both survived the brutal confrontation and went on to continue the contest between their Legions for control of the Aegis Sub-sector.
When next they fought, the Dark Angels executed a meticulously planned ambush on the Night Lords' fleet while it was in transit across the sub-sector that saw the back of the Night Lords Legion broken and their Primarch mortally wounded after having faced his brother El'Jonson once again in mortal combat. Thanks to skilled coordination and superb execution by the Lion, the entirety of the Legio Ulricon 's fleet was annihilated, causing their doomed vessels to spill their deadly cargo of Titans into space, which caused devastating losses to the Night Lords fleet.
The result of this disaster was the loss of dozens of VIIIth Legion capital ships and approximately one-quarter of their Legion fleet. Unfortunately, the remainder of the Night Lords fleet fled the Dark Angels' wrath, while the recently recovered Night Haunter, First Captain Sevatarion and the elite Night Lords Atramentar Terminators led a desperate boarding assault action upon the Dark Angels' flagship, the Invincible Reason.
This assault resulted in the death of all but a dozen of the Atramentar and the capture of Sevatarion and the remaining survivors. Konrad Curze fled El'Jonson's wrath, evading the Dark Angels for solar months, stalking the shadows within the bowels of their mighty flagship, avoiding the Dark Angels search parties and Lion El'Jonson himself. The Night Haunter would eventually effect his escape when the Dark Angels fleet made its way to Macragge in the Realm of Ultramar by following the beacon of the xenos device known as the Pharos on the world of Sotha.
Although the Night Lords suffered a devastating defeat, and the complete loss of the Legio Ulricon at the hands of the Dark Angels, their overall mission of protecting Horus' flank and delaying the Dark Angels reinforcement of Loyalist efforts to protect Terra was considered a success.
The three-year-long campaign delayed the Dark Angels long enough that by the time they defeated the Night Lords, and arrived at the Siege of Terra nearly five standard years later following their involvement in the Imperium Secundus project and the dissolution of the Ruinstorm, the conflict was already over.
The delay of the Dark Angels also had the added effect of distracting them from Luther's betrayal on the Dark Angels' homeworld of Caliban. Subsequently, this betrayal would result in the destruction of their homeworld in the days immediately after the end of the Heresy and would forever after steer the course of the Ist Legion and its later Successor Chapters in the pursuit of their wayward kin, the Fallen Angels.
The remnants of the Night Lords Legion eventually regrouped in the Eastern Fringe in the final years of the Heresy. They conducted a massive campaign of genocide and terror across the worlds of the Eastern Fringe of the galaxy the likes of which has never been seen before, or since. The Legion betrayed the increasingly self-destructive impulses which drove its Heretic Astartes, much as such impulses drove their Primarch.
The Night Haunter, almost slain twice during the Thramas Crusade, and distraught at the death of First Captain Sevatar, eventually escaped from Macragge, imprisonment by Lion El'Jonson and the travails of the Imperium Secundus. Curze fled to his dark lair on the planet of Tsagualsa, becoming a mad, naked, increasingly psychotic monster, until his assassination at the hands of the Callidus Assassin M'Shen.
With the death of their Primarch and their First Captain Sevatar, the Night Lords never really recovered from the losses of the Thramas Crusade. The Traitor Legion eventually broke up in the years after the Heresy into smaller warbands led by assorted Chaos Lords. Their presence in the Eastern Fringe thereafter diminished as many took refuge in the Eye of Terror like their fellow Heretic Astartes.
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