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The Mezoan Campaign, sometimes also referred to as the Third Siege of Mezoa, was a great battle fought in the opening years of the Horus Heresy. It marked the last concentrated effort of the Traitor Warmaster Horus Lupercal's forces to seize control of the strategically important Mechanicum Forge World of Mezoa, the last star system still loyal to the Throne of Terra in the Gothic Sector. Besieged by elements of both the Alpha Legion and Iron Warriors, Mezoa was only saved through the timely intervention of the Disciples of the Flames, a splinter-faction of the Salamanders Legion. The Third Siege of Mezoa is a visceral lesson in the remaining effectiveness of the Shattered Legions, those Legiones Astartes broken or annihilated at the Drop Site Massacre who were still able to intervene and hinder the Warmaster's carefully-laid plans. While few at the time saw little significance in the Loyalist victory, the actions of the Shattered Legions proved successful in slowing Horus' march towards Terra. The Mezoan Campaign also provides one of the few reliable accounts of the actions of Blackshield forces during the conflict.

War in the Coronid DeepsEdit

Following the revelation of the Warmaster's true intent in the Istvaan System, the worlds of the Coronid Deeps were the first to suffer from the Traitors' expansive efforts. Led by the Warmaster himself, the Sons of Horus quickly captured the heavily industrialised Manachean Commonwealth in the short-lived Manachean War, whilst their allies in the Death Guard under the command of their own Primarch Mortarion cleansed the strategically less important Grail Abyss of all life. Most importantly, through the events of the Treachery at Port Maw, the Warmaster captured a sizable naval fortress and orbital shipyard which would allow him to rearm and repair his fleets on the long march to Terra. By the end of 008.M31 only a few Imperial domains were spared the wrath of the Traitors' armies. To the galactic west, the isolated worlds of the Agathean Domain were deemed too insignificant to squander valuable military resources on conquering it, while in the Cyclops Cluster the Forge World of Mezoa proved a far too difficult target to assail readily. As the Great Crusade had done centuries before, the Traitors' advance would circumvent Mezoa and blockade it until enough men and resources could be gathered to take the strategically important domain of the Mechanicum.

While many worlds of these far-flung territories were deemed not valuable enough to offer any kind of coordinated resistance or threat -- which at least in the case of the Agathean Domain would prove to be a gross miscalculation -- the Warmaster knew that he could not ignore the powerful Mezoan Mechanicum. However, having challenged his father for the rule of the entire Imperium of Mankind, Horus, the pretender, could not afford to be delayed in the Coronid Deeps, but had to be seen on the frontlines, leading new conquests and rallying new star systems to his banner. The task of eliminating the threat posed by the Loyalist Forge World would be handed down to other military commanders belonging to the Warmaster's allies. Yet such a general could not readily be found. Horus' own puppet-ruler, Taloc Thorne, the Tyrant of Port Maw, lacked the military forces to both maintain productivity in the Manachean Commonwealth and conduct a military campaign of the scale required to conquer the belligerent Forge World. Horus' principal ally in the region, the Dark Mechanicum Forge World of Cyclothrathe, preferred to accomplish its own objectives rather than obey Thorne's orders. In truth, only the Forge World of M'Pandex, a long-time rival of Mezoa, showed any devotion to the Loyalists' eradication. But long eclipsed by its rival, M'Pandex too lacked the military resources to vanquish Mezoa alone. Two previous attempts to seize Mezoa's principal forge-fane had already been repelled, the Mezoan Magi using their world's own volcanic might against the invaders, letting the ground collapse under the Traitor's landing zones and rerouting lava-streams to stall any advance or burn their enemies to ashes. Some of the most exotic reports of the earlier campaigns from the survivors even told of kilometer-long chunks of solidified magma, essentially man-made asteroids, that had been flung as projectiles at incoming enemy ships. The kinetic impact alone had been powerful enough to break a voidship in two.

The Poisoned ChaliceEdit

Even as the wars of the Horus Heresy unfolded, the defiant Forge World still resisted every attempt at conquest by the Traitors. Words of Mezoa's continued defiance did not fail to reach Horus, and it is said that his wrath was terrifying to behold. Those records captured by the servants of the Emperor in the wake of the Warmaster's defeat attest of a vast armada gathering at Port Maw, where the fleets of those Legions loyal to Horus were refitted and repaired with the materials once intended to ensure the progress of the Great Crusade. It was here that Horus' latest proclamation was presented to his generals -- a formal order to destroy Mezoa. This order was so widely promulgated that several illuminated copies of this manuscript have survived to this day and are actually preserved in both the Imperial Archives of Terra and the Inquisitorial Archives on Tethys.

The elimination of the threat posed by the Loyalist Forge World was a necessity. With his armies mustering for their final push towards the Segmentum Solar, the Warmaster could not allow any potential weakness in his rear, or risk exposing the Traitors' vulnerable supply lines. But however important the conquest of Mezoa, every Traitor commander present at Port Maw knew that victory would only be achieved at a tremendous cost in lives and materiel. As a result of Mezoa's tectonic instability, the powerful God-engines of the Collegia Titanica could not be deployed, dramatically increasing the cost of taking the defiant Forge World. With much glory to be won in the oncoming wars, Horus' commanders were loath to weaken their forces at such an early juncture. Yet, none were so foolish as to openly refuse or ignore the will of the Warmaster.

Knowing that Horus' eyes rested upon them, a silent war of influence erupted between the commanders of the Traitor forces. Through veiled threats, outright lies and no few fatal confrontations, the officers of the Archtraitor's armies each sought to see the mission assigned to one of their rivals. For solar weeks this silent war went on, until the proverbial scapegoats presented themselves at Port Maw. Humbled by their defeat at the hands of the Shattered Legions during the Siege of Epsilon-Stranivar IX -- colloquially known as "Fortress Stranivar" -- the 78th Chapter of the Alpha Legion under their Consul-Delegatus Autilon Skorr and the depleted 114th Grand Battalion of the Iron Warriors arrived at Port Maw. In the absence of their respective Primarchs, both formations lacked influential patronage or an unified officer cadre that would have been able to oppose the alliance of previously established commanders. So it came to pass that these forces would have to take up the poisoned chalice and prosecute the Mezoan Campaign to its conclusion. In recognition of his rank, Autilon Skor was appointed as overall commander of the new taskforce and given access to Port Maw's vast stockpiles of arms and materiel.

Even in the wake of his defeat on Stranivar, Autilon Skorr's ambition was undimmed. Being fully aware of the enmity borne for him by most of the command elements of the 114th Grand Battalion, Consul-Delegatus Skorr used his new position as commanding officer of the Mezoan taskforce to appropriate the lion's share of the available resources for his own 78th Chapter, leaving the Iron Warriors elements under Nârik Dreygur little chance to recover from their previous losses. With the bulk of the IV Legion and their volatile lord, the Primarch Perturabo, deployed far away, Dreygur's pleas for help or materiel fell on deaf ears, the other commanders seeing little interest or profit in aiding one they regarded as a failed officer. With no other choice left to them, Dreygur and his Iron Warriors had to make what repairs they could and tend to their wounds, their resentment against Skorr growing even deeper.

Composed of a dozen capital class warships -- including a pair of the fearsome Mangonel-class Bombardment Cruisers, 9,000 Legiones Astartes, three full Taghmata from the Renegade Forge World of M'Pandex and 20,000 auxiliary troops, the Mezoa task force was one of the largest battlegroups assigned to an independent command that was not under the control of a Primarch. Knowing that victory in this particular theatre of war would ensure gaining the favours of the Warmaster, an invaluable commodity once Horus sat upon the Golden Throne, Autilon Skorr began his preparations. Departing in good order, the fleet entered the Warp, the Davinite Lodge Priests attached to the fleet's Navigator-contingent assuring Skorr that their passage would be swift and sure and cleared of all storms. In a few short solar days, the fleet entered the Mezoa System, but they soon discovered that they were not the first to arrive...

Devils from the Outer DarkEdit

"All things must be tested upon the anvil and beaten until the heart of their being is exposed and measured. This is true of loyalty as it is of steel, for loyalty that is never tested is as worthless as flawed metal."
— Codicil 13:9 of the Book of Vulkan

As one of the few bastions of Imperial resistance, the Forge World of Mezoa had been reinforced by splinter forces of the Shattered Legions and even Loyalist survivors of the Armada Imperialis which had been present at the Treachery at Port Maw. While welcome, these reinforcements failed to considerably alter the balance of strength. The mighty Forge World, a glowing ember encircled by a dense ring of orbital defence stations and kill-satellites, could not hope to match the Traitors' numbers. Even worse, Autilon Skorr had learned his lessons from the fiasco at the Siege of Epsilon-Stranivar IX and ensured that all his voidships' captains would obey his word, while the Loyalists' command -- even though united by a common goal -- was fractured. Nevertheless, the rag-tag Loyalist fleet bravely opposed Skorr's attempts to gain local space superiority. Soon, a chaotic void battle developed where the vessels of the Iron Warriors and Alpha Legion -- numbering more heavy Cruisers -- started to gain the ascendency. It was then that a new force emerged unheralded from the Warp at the very edge of the Mezoan System. Unsure as to which side the newly arrived ship would declare its allegiance, the battle ebbed, no new explosions illuminating the void as both sides turned their powerful Augur banks toward the unidentified warship that had emerged behind the Traitors' battleline.

On the bridge of the lone Legiones Astartes Strike Cruiser, the sensor and Vox-operators strove to make sense of the myriad jumbled identification markers and hails broadcast by the combatants. Several tense solar seconds passed while the ship's command crew tried to distinguish friend from foe, a period of time that could have seen the lone Cruiser quickly crippled had its arrival not plunged the Traitors' fleet into total disarray. With the situation now clear, the crew of the Salamanders Strike Cruiser Ebon Drake unleashed its batteries at the closest Traitor vessel, trying to manoeuver its way to join the Loyalist fleet standing sentinel over Mezoa.

Even with the arrival of the Ebon Drake, the Loyalists remained at a serious disadvantage in terms of both numbers and tonnage, but the Salamanders' arrival had disrupted the enemy advance and so the void-battle raged on for more than nine solar hours, both sides locked in a bloody stalemate. In the end, Skorr's unified command broke the balance, the Loyalists' fractious nature causing some ships to retreat and thus leaving their allies unsupported. Rather than face annihilation, the combined Loyalist fleet had to abandon the orbital space around Mezoa, regrouping at the system's outer planets. Several vessels, amongst them the Ebon Drake. chose to dare the enemy fleets' guns one last time and close with the Forge World, risking being crippled to release fights of landing craft and Drop Pods intended to reinforce the defenders on the ground. Of the half dozen Legion and Armada Imperialis vessels to attempt the manoeuvre, only three rose again, the rest annihilated by the Traitors' guns. With the Loyalist fleet in full retreat, no one could stop the great Mangonel-class Bombardment Cruisers and wallowing troop barges from closing with the Forge World, as Mezoa's orbital defences were soon swept clear by the combined fire of the Alpha Legion and Iron Warriors. The final invasion of Mezoa had begun.

The Gift of MezoaEdit

High above Mezoa, their path now unimpeded, the Bombardment Cruisers and troop transports carrying the Traitors' moved into position, while on the ground Battlegroup Revenant, comprised of the recently disembarked Shattered Legionaries from the Ebon Drake, gathered around their leader: Cassian Vaughn, former Legion Commander of the Salamanders' Legion in the days before its reunification with its Primarch Vulkan. Believed slain during the Drop Site Massacre, Vaughn had been unearthed by his brothers of the XVIII Legion and his armoured body had slowly but steadily self-repaired thanks to the techno-arcana crafted by Vulkan and his placement within the sarcophagus of a powerful Dreadnought. The Venerable Dreadnought had led his Disciples of the Flame to Mezoa's central forge-fane. There, the twice-dead former master of the XVIII Legion had met with the Norn-regents of Mezoa, a triad of truly ancient Mechanicum Archmagi-sisters so interlinked by complex neural interface technology that for all intents and purposes they formed a single entity which directed the vast domains of Mezoa. This historic meeting was immortalised by Mezoa's scribe-adepts and still remains in the data-archives of Mezoa ten thousand standard years later. The fire-blackened and battered armoured sarcophagus of Cassian Vaughn, the Dracos Revenant, confronted the deadly thin forms of the Norn-regents, each one of the three Magi suspended like spiders in the complex web of arcane cybernetic technology that allowed them to communicate and direct their thralls all across Mezoa. None can deny that the changed Cassian Dracos exerted some strange influence on every automata in his vicinity, for when he penetrated the Norn-regents throne-room, even the regents' personal bodyguard, towering and powerful Domitar-class Battle-Automata, fell back in halting steps, and who can say if the Norn-regents themselves were not somehow influenced by Vaughn's new aura?

Before the Norn-regents, Cassian Dracos spoke of his visions and of the trials he had endured as he lay buried under the black sands of Istvaan V. He told them of his search for Vulkan and his conviction that the Primarch of the XVIII Legion had yet cheated death. Cassian's tale of woe and sacrifice doubtlessly moved the Norn-regents, as the Salamanders' legendary tenacity somewhat echoed the Path of the Flame Eternal, the strange schismatic creed of the Cult Mechanicus honoured by both the Magi of Mezoa and the Hierarchs of House Hermetika. However, these similarities in belief and common loyalty to the Emperor of Mankind seem a rather slim basis for the accord that would be signed by Dracos and the Norn-queens of Mezoa. In this agreement, Cassian Vaughn was formally recognised as a living avatar of the Machine God and given command over Mezoa's sizeable Taghmata and its allies. For the dour Tech-adepts of the Mezoan forge-fanes, the unexpected arrival of a prophet of the Omnissiah was marked as a sign of their impending victory. Imperial scholars in later millennia have often wondered at the sudden acceptance with which Dracos was met by the different groups and factions he encountered. Some even suggested that this outcome might in some way be related to an ability bestowed by the Warp, as Istvaan V's position at the time of Cassian Dracos' near-death had it located at the heart of one of the fiercest Warp Storms in human record. Given the immense amount of blood shed during the Drop Site Massacre and its effects on the powers of the Warp, who can say for sure that the baleful powers of the Warp had not had a more serious effect on the entombed Dreadnought?

Whatever the truth, this alliance would prove beneficial for both parties. Unable to deliver the products of its forges to those Imperial units prosecuting the Great Crusade as they were intended to, Mezoa's storage vaults harboured a true fortune in suits of Power Armour, weapons, ammunition and armoured vehicles to which the Disciple of the Flames and other Loyalist survivors were now given access. In defiance of the ancient treaties negotiated with distant Mars and Terra which regulated who and in what quantity someone might receive the labour of Mezoa's forges, Battlegroup Revenant was entirely reequipped with the very finest of Mezoa's creations. Where previously most of the Shattered Legionaries could only rely on their own personal Bolters and those few man-portable heavy weapons they had brought with them, the Disciple of the Flames and their allies now had access to large stockpiles of armoured vehicles and personnel carriers, including the advanced command version of the venerable Rhino STC, the Damocles Command Rhino, which had only recently been approved for construction and had as yet not been delivered to any of the Space Marine Legions.

The greatest gift of all was perhaps a handful of newly-completed Glaive Super-Heavy Special Weapon Tanks initially intended for the IX Legion. Most notoriously, one of their number, the Dragon Eternal -- crewed by Xiaphas Jurr's Disciple of the Flame -- defended the Septurn Gateway of Mezoa's principal forge-fane for more than four solar hours after an Alpha Legion diversionary attack had drawn away the gate's other defenders. Attended by the most skilled of Mezoa's forge-wright, the Iron Dragon withdrew to the deepest and most sacred fanes of Mezoa in order to receive the benedictions of the Machine God that would mark his ascension at the head of the Mezoan Taghmata.

The Archmagi were also confident that they would be able to restore Cassian Dracos to his former glory, allowing the newly appointed Avatar of the Sacred Flame to walk again upon the battlefield. While outside the Traitors' dropships blackened the sky, it fell to Lieutenant-Chaplain Xiaphas Jurr to lead the Disciples of the Flame in battle against the attackers. However, they would not face the enemy alone. With them stood those members of the Iron Hands and Raven Guard Legions who had already travelled with them aboard the Ebon Drake, as well as forty-eight Astartes of the Imperial Fists, the survivors of the VII Legion's garrison on Manachea Lux whose flight had ended at Mezoa. Similarly, the 891st Lethe Cohort of the Solar Auxilia had also been drawn to the still-resisting Forge World and now stood ready to defend it against the closing Alpha Legion and Iron Warriors. Finally, Mezoa mustered its own defence forces in the figure of the Mezoan Taghmata, battle-automata of diverse classes and models, all veterans of centuries of xenos raids before the eradication of the Mitu Conglomerate. In total, it has been estimated that the defenders of Mezoa numbered close to 12,000 men-under-arms, including the cybernetic monsters, towering Battle-Automata and soul-shorn Adsecularis Auxilia of the Taghmata Mezoa and several dozen Knights of House Hermetika.

Onto the Crucible of WarEdit

For historians, most of the great battles of the Horus Heresy are difficult to reconstitute: too much data has been lost in the fires of that conflict or through the slow erosion of time. Even more has been sequestered purposefully by the authority of the Holy Ordos of the Inquisition or following the Edicts of the High Lords of Terra. It is fortunate that this is not the case for the Third Siege of Mezoa. Of these sources, the greatest wealth of information comes from the war chronicles of Nârik Dreygur, the de facto commander of the Iron Warriors' 114th Grand Battalion.

Although numbering in the thousands of vessels, the first wave of enemy dropships essentially carried pact-conscripts from Moab and other Imperial Army troopers who had declared for the Warmaster. Both were considered inherently expendable by their Legiones Astartes overlords, especially Autilon Skorr who commanded the Traitor armada. No defence cannons or flights of slaved Mechanicum drone-interceptors met the incoming assault wave -- Mezoa's guns remained eerily silent as the Magi had decided to turn to far more dangerous weapons: the wrath of Mezoa itself. Set deep beneath the stable crust of Mezoa's outer mantle, great subduction furnaces were used to hurl vast projectiles of magma and bedrock into the skies, each projectile easily measuring a kilometre in length. Against this weapon, the Traitor gunships and dropcraft stood no chance and the casualties proved devastating. Those few dropships that did manage to safely land on the ash-covered surface were eagerly awaited by packs of vicious Vorax-class Battle-Automata. Their Power Blades massacred the isolated Traitors and chased the scattered survivors into the caves and sulphurous crevasses of Mezoa's mantle where they would slowly choke to death, brought low by the heat, ash and toxic gases released by Mezoa's intense volcanic activity. Of the Traitor invasion's first assault wave, none survived, but unfortunately for the Loyalists, its intent was never to establish a proper beachhead but to provoke just such an aggressive response.

The Last BattleEdit


  • The Horus Heresy - Book Six: Retribution (Forge World Series) by Alan Bligh, pp. 33-53

Battles of the Horus Heresy
005-006.M31 Istvaan III AtrocityBurning of ProsperoWar Within the WebwayBattle of the Somnus CitadelUnrest on CalibanSignus CampaignSchism of MarsBattle of DiamatDrop Site MassacreFirst Battle of ParamarBattle of the Coronid Deeps
007-008.M31 Battle of PhallBattle of RavendelveBattle of the Alaxxes NebulaSiege of the Perfect FortressChondax CampaignSecond Battle of ProsperoFirst Siege of Hydra CordatusBattle of the Furious AbyssBattle of CalthBattle of ArmaturaShadow CrusadePercepton CampaignBattle of IydrisThramas CrusadeFall of Baztel IIIBattle of VannaheimInvasion of Paramar VBattle of Constanix IISiege of Epsilon-Stranivar IXTreachery at Port MawManachean WarMezoan CampaignBattle of BodtBattle of DwellBattle of Molech
009-010.M31 Xana IncursionCarnage of MoroxSangraal CampaignBattle of ArissakBattle of PerditusBattle of SothaScouring of Gilden's StarBattle of NyrconBattle of TallarnBattle of NocturneSolar WarBattle of Pluto
011-014.M31 Battle of YarantMalagant ConflictBattle of the Kalium GateBattle of CatallusBattle of ZepathBattle of KallethBattle of DesperationBattle of Beta-GarmonBattle of TerraGreat Scouring

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