Very little is known about the Tenebrae in current Imperial records other than that they fell to the service of Chaos in the centuries following the end of the Horus Heresy and that they are the rare band of Heretic Astartes that still maintains several Fellblades in active service.
The earliest surviving records of the Heretic Astartes force known as the Tenebrae name them as the hand behind the infamous "Hour of Shadow," which plunged the Hive World of Lorin Alpha into murder and madness in 118.M33, and whose anniversary is still marked by sorrowful mourning seven millennia later.
These records, culled from the archives of the Black Wings Chapter whose own Chapter Master was slain there, speak of the Tenebrae as already hated and reviled before this atrocity, but frustratingly the Inquisitorial eye of the present day offers no further leads to trace their origins further back in time.
The Tenebrae appear again and again, scattered through history, at the Luxor Drift Genocide, the Fall of Yun, the Plague of Madness and the Kharthah-Iconoclasm, right up to their most recent sighting during the Orpheus Crisis of 998.M41.
Always they appear during times of terror and discord, always their presence is a herald of suffering and the nightmarish distortion of reality as a wave of suicidal despair and insanity going before them like a baleful shadow.
Their dusk-purple armour bears little to indicate their true allegiance or origin, and their company is fled from even by others devoted to the Ruinous Powers less they become infected by whatever dark malignance has swallowed the Tenebrae and made them its own.
Where they go, light is consumed by darkness, a darkness which hungers for life and whispers blasphemies to eat at the sanity of the most righteous man. So insidious is this attack upon the will and the soul that when the Tenebrae attack in full force, for theirs is also the full panoply of war known to the fallen Adeptus Astartes, including many ancient relics of battle and daemon-tainted engines.
Little resistance can be offered against their onslaught and Fortress-Worlds and bastions thought secure against the might of armies fall in mere hours of dark butchery.
- The Hour of Shadow (118.M33) - After the Chapter Master of the Black Wings is murdered during the world of Lorin Alpha's Hour of Shadow, the Chapter chases a band of Tenebrae Heretic Astartes into the Veiled Region. Three standard centuries later, a single damaged Astartes Strike Cruiser returns bearing only a handful of survivors. They will speak with none save the agents of the Inquisition's Ordo Malleus and swear an oath of vendetta against The Tenebrae.
- The Death of the Witching Moon (013.M41) - The Forge Moon of Keziah, in the strategically vital Agathon System, fell into an unnatural eclipse when its population is driven to murder and madness in an endless night of horror. The dread forces of The Tenebrae and the Company of Misery reign as dark kings amid the nightmare, and the baleful light of the "Witching Moon" that Keziah has become spreads calamity and Warp-tainted phenomena wherever it now falls, threatening the entire star system. The first Imperial attacks by the Astra Militarum, squadrons from Battlefleet Ultima and the Inquisition are hurled back in tatters by the madness of the black light and the Warp-fuelled savagery of the defenders. It is only by the unexpected arrival of the Charnel Guard Chapter, accompanied by a sacred band from the Adepta Sororitas' Order of the Black Sepulchre bearing the holy relic known as the Book of Tears before them, that the imminent loss of tens of billions of lives on Agathon Prime is prevented, and the insanity-inducing radiance of the Witching Moon is held back. The Charnel Guard lead a fresh assault as further Adeptus Astartes forces, including the Iron Hands, Storm Lords and Angels Porphyr, and Adeptus Mechanicus reinforcements arrive, fighting a brutal battle of tank and gunship clashes across the soaring metal canyons which crease the moon's surface and chamber-by-chamber Zone Mortalis actions to purge Keziah of the shadow that has befallen it. The Traitor Marines inflict fearful losses on their besiegers before they are driven into the deeper darkness of the Warp. In the wake of their retreat, all life is purged from Keziah before it is given back to the hands of the Machine Cult for tech-exorcism and eventual reclamation.
The warband colours of the Tenebrae are dusk-purple.
The warband badge of the Tenebrae is unknown in current Imperial records.
- Codex Heretic Astartes - Chaos Space Marines (8th Edition), pg. 50
- Imperial Armour Volume Two (Second Edition) - War Machines of the Adeptus Astartes, pg. 17
- Imperial Armour Volume Thirteen - War Machines of the Lost and the Damned, pp. 56, 58