One eternal evil sparked the Horus Heresy, laying low the Warmaster – the Anathame.
An anathame was a unique sword-like weapon produced by a xenos race called the Kinebrach. Several came into the possession of the Interex, where they were encountered by the 63rd Expeditionary Fleet of the Imperium during the Great Crusade.
At first glance, an anathame was a simple knife or sword with a napped flint blade and golden hilt. The weapons appeared to be semi-sentient, as the Interex claimed the weapons could be instructed to recognize a particular person, which gave them the ability to mortally wound that person. The Interex did not know how to produce these weapons, but had confiscated them from the Kinebrach. At least one was on display at the Hall of Devices on Xenobia Principis. When Word Bearers First Chaplain Erebus stole it and destroyed the Hall, the Interex accused Warmaster Horus‘s party of the crime, sparking the Battle of Xenobia Principis.
Erebus took the anathame to the moon of Davin and gave it to the already Chaos-tainted governor Eugen Temba. When Horus led the 63rd Expeditionary Fleet back to Davin to return it to compliance, he confronted Temba on the moon. When Horus would not side with him, Temba spoke his name to the anathame and attacked with an agility that could not have come from his bloated, decaying body, driving the blade through the Warmaster‘s left shoulder before Horus slew him.
Had it been any other weapon, Horus would have survived and healed normally, but the anathame had his name and Horus’s Astartes physiology could not heal its wound. The Mournival brought him to the medicae deck aboard the Vengeful Spirit, where Apothecary Vaddon determined that Horus’s Larraman Cells were not functioning, preventing Horus’s shoulder wound from clotting. Vaddon told Garviel Loken that he might be able to save Horus if he could examine the weapon which wounded him, So Loken, Tarik Torgaddon, Nero Vipus, and the members of Locasta Squad went down to the surface of Davin’s moon to search for it.
The search party found the anathame and brought it to Vaddon, with Loken giving him explicit orders not to mention its existence to anyone. Fabius Bile presented the Warmaster’s Seal to Vaddon and took the anathame from him, delivering it to his primarch Fulgrim. Shortly before the betrayal at Isstvan III, Fulgrim used the anathame to kill Commander Vespasian. He later used it to kill remembrancer Ostian Delafour in his studio, impaling him through a painstakingly-sculpted statue of the Emperor. Fulgrim left Ostian and the anathame, where Serena D’Angelus would later kill herself on the protruding blade.
First Chaplain Erebus forged eight athames from the anathame weapon that he had stolen from the Interex, and which later turned Horus to the worship of Chaos. He kept one for himself and gifted the others to the commanders of the Word Bearers Host on Calth; Kor Phaeron, Morpal Cxir, Foedrall Fell, Hol Beloth, Quor Vondar, and Phael Rabor, and the last one for his own bodyguard commander, Kolos Undil.
When passing these out, Erebus warned the assembled commanders that these were no “ordinary” athames, indicating that the athame was a name used by the Word Bearers even before Erebus acquired the anathame.
Criol Fowst, a human leader of the Brotherhood of the Knife, possessed an athame gifted to him by his Legionary patron, Arune Xen. Fowst used his athame to sacrifice victims as part of the Word Bearers’ summoning ritual. He considered it his most treasured possession, and was enraged when he lost it to Oll Persson. Persson later used this athame to cut a rift in realspace that allowed him and a small group of survivors to escape the poisoning of Calth‘s atmosphere.
Ultramarines Captain Remus Ventanus was able to kill the daemon Samus with an athame confiscated from Morpal Cxir. He used the knife because he had no other weapon to hand, but was amazed by its potency in killing the daemon. His Sergeant, Kiuz Selaton, suggested gathering the other fallen daggers and using them against the hordes of daemons rampaging across Calth. Ventanus considered using them might have a corrupting influence and refused, but kept the one he had used on Samus in his belt.
Kor Phaeron and his elite guard carried athames during their boarding action of the Ultramarines’ orbital weapons platform. When Roboute Guilliman and a small force of Ultramarines boarded the platform, Phaeron was able to stun Guilliman with his sorcerous powers. While the Ultramarines’ Primarch was temporarily helpless, Phaeron became intoxicated with the idea of using his athame to turn him to Chaos, just as Erebus had turned Horus. He pierced the flesh of Guilliman’s throat with it, but didn’t strike a fatal blow. That was his mistake: resistant to whatever dark influence was carried by the knife, Guilliman counter-attacked, driving Phaeron back and forcing the Word Bearers to retreat.
Kor Phaeron used his athame to great effect in the subsequent Battle of the Macragge’s Honour, cutting a “hole” in realspace that allowed the battleship Infidus Imperator to make an instant translation into the warp, without the need for the normal calculations. Later, when the Macragge’s Honour devastated the Infidus Imperator with an overwhelming volley, Phaeron cut another hole that allowed him and a small entourage to escape the bridge of his doomed ship, to reappear on Sicarus.
Later, during the Underworld War, Ventanus slew Hol Beloth with Beloth’s own athame.
Post Heresy Appearances
Ten thousand years later, during the Invasion of Ultramar, Marneus Calgar, the Chapter Master of the Ultramarines, killed the Daemon Prince M’kar with the athame that Uriel Ventris had retrieved from Captain Ventanus’ tomb. The Daemon recognized the knife as the Shard of Erebus. This knife was likely the same athame that Ventanus had taken from Hol Beloth, though it could also have been the knife Ventanus had taken from Morpal Cxir and used to banish Samus.
In M41, an operative of the Ordo Malleus stole an athame from a museum on a Tau Sept World; the Tau had mistaken it for a crude flint knife, proof of how little the gue’la had evolved over their long history, and had no idea of its special properties. When trapped by a team of Fire Warriors, the operative used the knife to “cut a hole in reality” and escape
~The idea that a stone knife could lay low a Primarch is foolishness. Report anyone spreading such rumors to the Inquisition immediately.