The 9th Black Crusade was a Black Crusade led by the infamous Chaos Champion Abaddon the Despoiler and his Black Legion, launched out of the Eye of Terror in 537.M38. Intending to bring about the demise of the naval fortress of Cancephalus, Abaddon led his forces against the heaving populations of the nearby world of Antecanis.
Monarchhive, the hive city that served as the seat of Antecanis' Imperial Commander, was besieged by Abaddon's vanguard. The Black Legionaries burned and butchered their way through the lower levels, whilst Abaddon himself stormed its inner sanctums. The hive populations were slowly destroyed by the slaughter.
By the time the forces of the Astra Militarum arrived from Cancephalus to reinforce the desperate survivors, Abaddon and his favoured Legionaries had already left orbit, dropping a dozen Cyclonic warheads onto the ruins of Monarchhive in a last gesture of contempt.
The seventeen-standard-year-long war that ensued robbed both Antecanis and Cancephalus of their most precious resource -- manpower. Without the fleets of Cancephalus to stop him, Abaddon was able to ravage the rest of the sector at will , and his Sorcerers were free to conduct the rituals required to weaken the walls of reality in that region of space with impunity.
During this time, the Lamenters Space Marine Chapter was recalled along with a number of other Crusading Chapters by the High Lords of Terra to help deal with the rising threat of incursions from the Eye of Terror. Fierce fighting that saw the extinction of two Chapters (coincidentally both named the Celestial Swords by some error of the Adeptus Administratum) ensued throughout the sector.
The Lamenters' fell reputation for suffering bitter reversals and dark turns of fate worked against them during their defence of the Hive World of Corillia from a Chaos attack.
The superstition-bound Mortifactors Chapter refused to fight alongside the Lamenters, abandoning the planet rather than serve besides fellow Astartes they considered cursed. Unwilling to desert the Hive World's population, the Lamenters held out alone against the Black Legion's onslaught for six solar weeks, suffering horrendous losses until the Ultramarines and White Scars led an Imperial battle group that broke though the Chaos warfleet to relieve Corillia.
Reduced to barely 200 surviving Battle-Brothers by their sacrifice, the Lamenters were deemed lost when their fleet disappeared into a Warp Storm soon afterwards, only to reappear more than a standard century later on the edge of the Segmentum Solar, having slowly battled their way back from the outer void.
- Black Legion: A Codex Chaos Space Marines Supplement (6th Edition) (Digital Edition), pp. 37, 39
- Codex Adeptus Astartes - Space Marines (8th Edition), "Unknown Foundings - A Legacy Reforged", pg. 59
- Codex Heretic Astartes - Chaos Space Marines (8th Edition), "Legacy of Hate," pg. 23
- Codex: Chaos Space Marines (6th Edition), pp. 23, 73
- Imperial Armour Volume Nine - The Badab War - Part One, pp. 106, 108