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Treachery at Advex-Mors

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Treachery at Advex-Mors
Conflict Horus Heresy
Date 006.M31
Location Advex-Mors
Outcome Traitor pyrrhic victory
Traitors Loyalists
Unidentified Justaerin Consul(KIA) Knight-Praetor Kordray Mordred
At least on chapter
Conqueror's Pride
Several Stormbird and Storm Eagle squadrons
c. 1,500 Dark Angels (51st Chapter and Order of Broken Claws)
Xiphon Interceptors
Heavy Heavy

The Treachery at Advex-Mors was a battle of the Horus Heresy.[2] Fought in 006.M31, it is the earliest known engagement of the Dark Angels in the conflict.[1a] It was also known as the Battle of the Rangda System, as some chroniclers of the Horus Heresy knowingly or inadvertently misidentified Advex-Mors as the old homeworld of the Rangda Xenos.[1a][2]


The Rangdan Xenocides were among the most catastrophic wars of the Great Crusade, and brought the Imperium to the brink of destruction. In fact, the conflicts were so terrible that much information about them was suppressed or destroyed after the Imperials finally claimed victory. The nature of this victory itself was highly disputed, and many conflicting accounts existed about the final Rangdan Xenocide.[1b]

The Dark Angels created the Order of Broken Claws during the Xenocides; this cadre of warriors had the specific task of fighting the Rangdan Xenos. Even though the Order faded in importance after the Imperium claimed to have destroyed the entire species, it was not disbanded and instead continued to guard a station on Advex-Mors where the Rangda had first been encountered by the Imperium.[1b] Some accounts would later misidentify this world as the Rangdan homeworld, allegedly purged during the Third Rangdan Xenocide.[1a]

The station at Advex-Mors harbored the secret knowledge and waeponry associated with the Rangda and the Xenocides.[1b] The 51st Dark Angels Chapter, known as the Sable Griffons, was tasked to guard and protect the Order of Broken Claws in turn. The Advex-Mors garrison was eternally vigilant for the possible return of the Rangda.[1a]


In 006.M31, the Dark Angels at Advex-Mors were hailed by the Sons of Horus Heavy Cruiser Conqueror's Pride which signaled it needed to resupply. Once in orbit, several squadrons of Stormbirds and Storm Eagles headed for the surface of Advex-Mors. Queries from the Dark Angels regarding their destination were ignored and when Knight-Praetor Kordray Mordred demanded to speak with the Sons of Horus commander, he was met with a sudden and indiscriminate barrage. The barrage left little of the Dark Angels fortifications intact yet inflicted only light damage on the chantry house of the Order of Broken Claws.[1a]

The outermost defenses crippled, the Sons of Horus gunships set down and disgorged a full Chapter including a company of Justaerin Terminators. The Sons of Horus advanced upon their shattered foe, committing only a token force to seize the Astropathic nexus. The Justaerin Consul himself tore the Chapter House gate from its hinges and dared the defenders within to come out against him. When none dared to come forth, the Justaerin marshalled their strength and entered the antechamber. At that moment, a great detonation spread across the entrance, causing great damage to the Sons of Horus and trapping them inside. It was then that the 12 surviving Dark Angels of the Order of Broken Claws attacked the nearly 50 Justaerin. Within the pitch-black labyrinthine corridors of the Chapter House, the Broken Claws broke the pride of the Warmaster and when Sons of Horus reinforcements managed to breach the rubble and arrive inside they found a mountain of their comrades corpses. The three surviving Dark Angels withdrew to the lower vaults where the relics of the Rangdan were held in stasis.[1a]

Their honour besmirched, the Sons of Horus refused to resort to simple solutions such as Promethium or Phosphex and instead selected the most skilled of their number to launch a direct attack. The first group consisted of veterans but only survived for ten minutes, felling a single Dark Angel defender. Three further bands of Sons of Horus descended and stilla single Dark Angel stood guard over the guard. Word then reached the rearguard that the Dark Angels survivors at the astropathic nexus had driven them from the core and had control of off-world communications. Finally, the Sons of Horus sent in their Destroyer Squads. The final Dark Angel gave a last salute before being consumed by Phosphex. The Sons of Horus Techmarines were able to scour the vault for valuable pieces of Rangdan technology, which had been their objective all along. The Conqueror's Pride subsequently launched a mass orbital bombardment to erase any trace of their attack. One of the grounded Stormbirds was captured and the relics it bore lost to a daring assault by Knight-Praetor Mordred and his Deathwing lifeguard, while another was shot down and destroyed by Ravenwing warriors piloting Xiphon Interceptors, though the survivors of the Sable Griffons could not halt the exodus of the Sons of Horus.[1a]

The remnants of the assault force reached orbit leaving the Dark Angels trapped below, but they could spare no time to exact any revenge, for the Promethean Class Cruiser Invidious had returned, called back from patrol by Knight-Praetor Mordred, and the Conqueror's Pride was no match for the ancient Terran warship in open battle. Bloodied in body and pride, the Sons of Horus fled the Advex-Mors system. They had come seeking both weapons for Horus' desperate rebellion and to break the will of one of the unquestionably loyal Legions but could claim little more than a pyrrhic victory.[1a] However, the potency of the captured waepons could turn the Horus Heresy in the Traitors' favor.[2]


Battles of the Horus Heresy
005-006.M31 Battle of Isstvan IIIFirst Battle of ProsperoWar Within the WebwayBattle of the Somnus CitadelUnrest on CalibanSchism of MarsBattle of DiamatDrop Site MassacreBattle of the Rangda SystemFirst Battle of ParamarManachean WarSignus CampaignTreachery at Advex-MorsSiege of CthoniaBattle for Felweather Keep‎
007-008.M31 Battle of PhallBattle of RavendelveRuin of MaerdanBattle of the Alaxxes NebulaPale Stars CampaignBreaking of the Perfect FortressChondax CampaignSecond Battle of ProsperoFirst Siege of Hydra CordatusBattle of the Furious AbyssBattle of CalthBattle of ArmaturaBetrayal at IthracaDeath of CanopusShadow CrusadeCrusade of IronDoom of BorminaDefence of TyrosDefence of the Three PlanetsBattle of UlixisAmbush at EspandorBattle of Aquila AtollBattle of Drooth IIPercepton CampaignBattle of IydrisThramas CrusadeFall of Baztel IIIBattle of VannaheimSecond Battle of ParamarBattle of Constanix IIMezoan CampaignBattle of BodtBattle of DwellErellian SubjugationSiege of Baal
009-010.M31 Battle of MolechBreaking of AnvillusXana IncursionCarnage of MoroxSangraal CampaignBattle of ArissakBattle of PerditusBattle of SothaDrussen AtrocityScouring of Gilden's StarBattle of NyrconBattle of TallarnCataclysm of IronBattle of NocturneWar of DrakesBattle of PlutoSiege of InwitBurning of Ohmn-MatBitter War
011-014.M31 Reaving of the Xibana ReachesLorin Alpha CampaignSubjugation of TyrinthMalagant ConflictBattle of the Kalium GateBattle of CatallusAxandrian IncidentBattle of the Haddon SystemJarrazr IncursionBattle of TralsakTarren SuppressionBalthor Sigma InterventionBattle of AbsolomScouring of the Ollanz ClusterBattle of ZepathSecond Battle of ZaramundBattle of AnuariBattle of PyrrhanSecond Battle of DavinArgolian MassacresBattle of TrisolianBattle of YarantBattle of KradeBattle of DelugeBattle of Heta-GladiusBattle of the Aragna ChainBattle of KallethBattle of the Diavanos SystemBattle of DesperationBattle of Beta-GarmonWar for AgaropsDefence of RyzaBattle of ThagriaPassage of AngelsThassos IncidentBattle of Zhao-ArkhadSerpent's CoilSiege of BarbarusForicaan CampaignBattle of VezdellBurning of VrexorDawn of DesolationDeath of ChemosBattle of Luth TyreYdursk IncidentFall of TenzebarSolar WarRaid on LunaSiege of TerraGreat Scouring