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The Treachery at Port Maw was a notable military defeat for the Imperium of Man during the earliest years of the Horus Heresy and what was later designated the Manachean War. It was by the twin assaults of the Traitors on Hive Illum and the Armada Imperialis Port Majoris of Port Maw that the Manachean War was concluded, marking the end of the powerful star system that had been the heart of the Manachean Commonwealth and the establishment of the first Traitor-held domain in the galaxy.

As far as the dire events of Istvaan III and Istvaan V revealed Horus' influence within the Legions of the Legiones Astartes, the Treachery at Port Maw is a testimony to how far Horus' treason ran within every other organisation -- military and civilian -- of the Imperium. To Imperial historians, the "Treachery at Port Maw" marks the beginning of a shadow war that has run its course for the last ten millennia, a fifth-columnist's and traitor's war that has since then become the hallmark of another Legion of Traitors: the Alpha Legion.


A Muster for War

The Manachean Commonwealth was an independent dominion forming its own self-governing sub-sector within the Imperium to the galactic East of the Cyclops Cluster. Considered the lynchpin of the Coronid Deeps, it was also the principal axis of Imperial power holding the northern border of the Imperium together thanks to the dual influence of two star systems: Manachea itself - principally the Hive World of Manachea Vysidae - which was in terms of population and industry the equal of any of the great Hive Worlds of the Segmentum Solar, and Port Maw which, while still under construction and expansion, was one of the most powerful Imperialis Armada bases in the northern Imperium. This border sub-sector, geared as it was for war, presented a formidable obstacle to any attack contemplated against it, and few regions outside the heartlands of the Segmentum Solar could claim to be so well protected.

Port Maw itself was home to a very sizable fleet, numbering some one hundred and seventy capital and line vessels of the first rank, and nearly a thousand other warships of lesser degree, whose principal purposes were to patrol the nearby Segmenta within the borders the Great Crusade had established; defend its worlds from attack, maintain order and enforce the writ of Imperial law. As part of this peacekeeping force, stationed there at secondary bastions in the Manachea and Numinal Systems, was a combined army of one hundred and ninety-three Solar Auxilia Cohorts of the Imperial Army, forming an independent strategic command of the Excertus Imperialis under Grand Admiral Ospheus LaBray.

In practical terms, this comprised notionally some 3,860,000 fully armed, equipped and disciplined soldiers outfitted to the highest standards of the Imperium's human soldiery. As Solar Auxilia, they were trained and experienced both in void combat and planetary defence operations, and represented a significant military force, even when set against the threat of a Legiones Astartes attack. Besides this elite army, the Commonwealth's own emergency defence planning was predicated upon the ability to quickly raise, arm and supply tens of millions of planetary militia in extremis, and this act itself did not seriously impact upon the massive economic output of the sector -- such were the immense labour reserves of Manachea Vysidae and the war matériel its wealth had allowed it to stockpile.

Nor was the Commonwealth entirely without the assistance of the Legiones Astartes, albeit in very small numbers. The limited garrison of Imperial Fists stationed in their bastion on Manachea Lux had quickly subdivided itself and sent its Legionaries to act as advisors throughout the Commonwealth, lending their expertise in counter-siege warfare to improve defensive structure and emergency action plans. However, those of the Astartes that had managed to escape the deadly trap set for them on Istvaan V refused to submit themselves to "merely" human commanders and had pursued their voyage, grateful for the opportunity to regroup and re-equip before moving on.

The question then immediately becomes: why did this vast and mobile force not come to the aid of the Cyclops Cluster when it was attacked? The answer is a simple one; it was not allowed to. The Warmaster Horus had not allowed it.

Long before the first shot was fired on Istvaan V, or even Istvaan III, the Warmaster had ensured that every centre of the Imperial military he could not control or vanquish immediately would be temporarily neutralised so as not to impede his first moves in the planned galactic civil war. So it was that at the time of the Istvaan III Atrocity, numerous elements of the Port Maw Excertus had been deployed to the very edges of their usual far-flung operational range; tied down in chasing half-unsubstantiated reports of privateers or xenos marauders, occupied on deep patrols or even temporarily reassigned to other campaigns or fleets in distant border regions of the Imperium -- whether such reinforcements were truly warranted or not. With the authority of the Warmaster still absolute and uncontested, such actions didn't raise any suspicion or comment. When the rebellion became apparent, orders were modified and warship squadrons and Cohorts of Solar Auxilia recalled at once for a grand muster at Port Maw, but this was a task neither swift nor easy. Marshalling troops also became increasingly more difficult as a great increase in Warp Storms and Warp turbulence was noted which would only gain in intensity as the Horus Heresy unfolded. By 006.M31 matters became ever more dire for the isolated Port Maw Excertus as its fleet elements had spent most of the previous years chasing shadows and were now confronted with a very real and terrible enemy. All across the Coronid Deeps, reports of isolated and unknown warships, civil unrest, outlaw activities, unexplained calamities and xenos raids became ever more frequent -- then came the messengers of the Warmaster, demanding the Dark Compliance of the Cyclops Cluster, the Grail Abyss and even Lethe within the borders of the Manachean Commonwealth. It was only a question of time until such an emissary would be sent to Manachea as well.

Yet no emissary came, but that seemed a small relief compared to the dire news that continued to reach Manachea. Many deep range patrols sent beyond the Segmentum border simply did not return, while raiders attacked Imperial outposts perilously close to the borders of the Coronid Prohibition Zone, an area of space where the authorities of Port Maw were forbidden to enter by ancient decree. These raids were tentatively attributed to the Rogue Trader Militant Rom Jhutlannder whose ships had served in the past as outriders and pathfinders for the Warmaster's own 63rd Expeditionary Fleet. However, when the enemy finally manifested itself, it would not be from the quarter expected, but from the western approach of the Commonwealth: a xenos-infested conglomerate of ancient ship-wrecks and trapped asteroids, a Space Hulk which the Manachean Commonwealth had not seen in many decades -- the Orks had invaded the Vlorath Srader System.

The Enemy Unlooked For

In accordance with the Coda Navis the invading Space Hulk was designated Red Polyphemus and its unexpected appearance sent the Commonwealth's military scrambling to respond. Space Hulks are immense conglomerations of shattered planetary rock and ancient derelict ships whose navigation is notoriously unpredictable. It was thought at the time that the Hulk had been drawn perhaps to the system's potent Astrotelepathic relay orbiting the system's seventh planet. However, its appearance after a brief but violent storm in the Warp seems too doubtful in hindsight to be considered as mere ill-fortune.

An Ork Space Hulk approaching an Imperial World

While the Orks as a galactic-scale threat within the expansive celestial territory of the Imperium had been subdued by the Great Crusade, on the outer frontier of the Emperor's domains, they still remained a potent if infrequent menace, and the degenerate, half-devolved breed that infested the Red Polyphemus represented the largest concentration of the brutal xenos encountered in the region for nearly thirty standard years. Such a dire menace required the immediate mustering and despatch of an entire battle group from Port Maw to combat, diverting a muster of warships and cohorts intended to deal with the worsening situation in the Cyclops Cluster. By the time the Imperial fleet answered the attack, the Vlorlath Srader Relay was already overrun, and tens of thousands of mutated Orks and gyre-worms had made planetfall on Vlorlath Srader while the Space Hulk itself ploughed madly onwards, forcing the fleet into a dogged and bloody pursuit. In normal circumstances, the aid of a sizable Legiones Astartes force would have been ideally called upon to strike a death blow to the Hulk, but in these darkening times, no such aid was available. This left the Port Maw battlegroup the thankless and dangerous task of attempting to slowly pulverise the gargantuan Red Polyphemus with prolonged, close-range bombardment, rather than board it and destroy it from within -- all the time under attack by the barbaric xenos which infested it like vermin. Without the elite Solar Auxilia Cohorts of the Port Maw Excertus Command, dealing with this catastrophe would simply not have been possible, both in terms of the counter-invasion of the Vlorlath Srader System's colony worlds, and the defence of the taskforce attacking the Ork Hulk, which faced continual suicide attacks and boarding assaults by the savage xenos and their crude but murderous void engines.

As the campaign against the xenos dragged on into the closing days of 007.M31, the Hulk finally began to fragment under the bombardment, but the victory's cost had entailed a butcher's bill in lives and voidships lost increasing with every report, while word reached Port Maw and Manachea of the fate that had befallen Lascal -- the destruction of an entire battlegroup of the Port Maw Armada -- and then Dominica Minor, offering a terrible blow to the Commonwealth's morale. The fears of the Commonwealth's defenders now had a name and a shape at last. Calls for military aid were passed on to still-loyal territories to the galactic East in the Coronid Reach -- the only part of the Imperium with which contact could be readily made now that the Astropathic relay of Vlorlath Srader was lost to them. Grudgingly such worlds like Numinal and Agathon gave their accord, well aware that should Port Maw fall, they themselves would have little chance to prevail on their own against this enemy. Orders for general mobilisation were issued, the final stages of emergency plans enacted, defences on the Commonwealth's eastern borders were heavily reinforced and known stable Warp termini to and from the Cyclops Cluster were aggressively laid with Void Mines. Given the ongoing battle within the Vlorlath System occupying a major part of the fleet's strength, the order was given that task forces and patrols were to be recalled where possible from all other posts and rendezvous at Port Maw with the expectation of having to meet head-on what would once have been an unthinkable threat: the direct and massed attack of the Death Guard Legion from the silence of the Cyclops Cluster.

It was, unfortunately, all just as Horus had planned.


The situation in the Port Maw System was one of extreme and ruthless order holding back a tide of chaos. The shell of the great artificial planetoid on which the vast Imperial naval base and void-forges had been built was choked by a swarm of vessels, both mighty and small, from a score of battleships girding themselves for war, to dozens of cruiser squadrons, countless hundreds of Escorts and thousands of servitor-drone tenders, victuallers and supply ships, troop transports and orbital lighters -- all about their own business as the entire star system stood on a state of high alert. In grim alliance, reinforcing fleets had come from the east, dark bronze warships bearing the fiery lantern-sigil of the Agathean Domain, one of the most isolated of all of the Imperium's clusters of human civilisation, lean pirate-killers from the Cerada Nebula and a trinity of huge storm-grey war-arks from the Mechanicum Forge World of Cyclothrathe, void-automata scuttling across their hulls like macabre insects.

Into this morass of vessels, before the border fell silent, had also come the refugees from the storm. Some had been mercantile vessels, other great livestock conveyors or ore transports, fleeing from a dozen different star systems under threat or under attack, and others were warships, the ragged survivors of the battles in the Cyclops Cluster. A handful had fled from as far afield as the murderous void battles at Istvaan, but of these no Space Marine vessels remained long at anchor. Of this flotsam of war, most had been mauled by the enemy or driven past any safe operational ability in the desperate flight to reach safety, and all required aid and assistance of some kind. Some even had arrived in such a parlous state that they had to be scuttled or set to drift at the system's edge so they posed no danger to the vortex of ships that swirled around the port station.

This hurricane of vessels, with its complexity and ever-shifting maze of hazards, was far too great a burden than any merely human mind could bear, and control of the vast armada was channelled through Port Maw's Mechanicum Astra Control Panopticon. This powerful broadcast tower, ten kilometres high, jutted spike-like from Port Maw's southern pole. From here fleet orders and beacon signals were relayed, navigational co-ordinates checked and rectified, and centrally controlled Cogitator-maintained data directly fed into the helms of the ships under Port Maw's watch, so as to swiftly reorganise their patterns and avoid collision. This system could, of course, be overridden by the ships themselves, but still represented a terrible vulnerability and so the Panopticon's control frequencies had been proofed against treachery by a complete replacement of cyphers and encryption-djinn following the reveal, first of the Warmaster Horus' treachery, and then changed again with panicked haste after the double blow of yet more betrayal at Istvaan V.

This had been of even greater concern as a significant portion of both the Raven Guard's and the Iron Warriors' fleets had made layover for resupply at Port Maw on their way to what would become the Drop Site Massacre, and both had been fully updated on the Port's codes and deployment schedules. All of this was deemed compromised and once again swiftly replaced wholesale and, due to this, the Port Maw Void Augury and geas-override systems were believed by the Armada Command to still be impregnable against outside influence. Indeed, perhaps they would have proved so, except that the spider at the heart of this vast web, the Archmagos Leit Mercuric, Cyber-Ordinator of Port Maw, was already secretly sworn to Horus.

The Web of Deceit

Under the hand of the treacherous Archmagos of Port Maw, a fiendish web of conspiracy and malevolence had been forming and its strands stretched far and wide across the Manachean Commonwealth and its worlds, and out to the dominions of Agathon and the dual suns of Cerada at the furthest extreme of the Coronid Reach. Now its hour was at hand.

This conspiracy had many layers and many agencies were bound up within it, from the Traitor Archmagos Astral Mercuric and her acolytes, to several officer cadres of the Imperialis Armada who had been corrupted by strange rites and secret societies brought into their midst while serving alongside the Sons of Horus and the Word Bearers Legions, to turncoats bribed through the more traditional means of festering dissent, greed, fear and hungry ambition, and purposefully planted spies and saboteurs hiding behind identities of murdered men and women. Their numbers, particularly in relation to the billions of men and women under arms in the Manachean Commonwealth, were in comparison very few, but they were well placed, and within such a tainted network, it had been all too easy to ensure that forces and agents loyal to the Warmaster were where they would do the most harm when the time came.

Like a fruit, wholesome to the appearance but canker-ridden from within, the Manachean Commonwealth's vaunted defences were already undermined and its fate was to serve as an object lesson not in outright destruction -- as that at the worlds of the Cyclops Cluster had been -- but in the surety of a blade in the back.

The Song of Chaos

At Port Maw, in the flickering actinic light and glimmering brass of the Mechanicum Control Panopticon, a countdown set in motion long before wound down finally to zero. The Mechanicum data-djinn web blazed with a power unheard of, and all over the system Vox-circuits burned out, Auguries were suddenly shrouded in static and Auspex scanners shut themselves down as if to avoid the flash-flare of a nova. The vast swirling fleet that surrounded the Port Maw station was in a moment all but blinded, and in that same moment, the navigational net entrusted to sift safe order from chaos began to lie. Ships collided without warning, showering wreckage in the paths of others, drives flared suddenly to full power, hurling the crews of the runaway vessels to bloody pulp, pulverised by the unexpected and unguarded against accelerations, and flag bridges were swamped with hostile scrap-code.

An Imperial vessel in high orbit above an unidentified world

On a hundred vessels, systems failed or misfired as the chaotic signal continued to pulse, and in the others whole decks depressurised or vented into the void, dragging their silently screaming inhabitants with them. The worse calamities the deadly electromagnetic song inflicted, though, fell upon only the lesser vessels; the merchantmen and the light Escorts without the power to resist and to whom an end came swiftly. The greater warships were far too powerful and too resilient to suffer much other than debilitation and confusion from this data-djinn-borne blade in the back, their own fearsome machine-anima immediately reacting against the attack, over-riding or burning out corrupted systems to regain full control. But as they recovered, many of these leviathans of war found themselves suddenly under fire from those they believed allies.

For while many reeled, there had been warships prepared in secret for this assault and others against whom the attack had not been directed at all and at whose helms Traitor hands had mastery. Already warships had begun to burn as former comrades opened fire at point blank range before they were aware of the danger, laid low by treacherous strikes intended to cripple rather than kill. Within tightly-formed squadron formations, Vox-broadcasts demanded surrender and some vessels, finding themselves surrounded by turncoats and all but powerless, could do nothing but comply. Elsewhere the initial attack had been anything but successful in subduing those ships that remained loyal, and aboard these, Void Shields swiftly ignited and alarm sirens sounded as battlestations was called with vengeful ire.

Emblem of the 905th Solar Auxilia Cohort

On the vast conglomerate station complex that was Port Maw itself, fighting had already broken out between Traitor and Loyalist, the station's provost marshals having thwarted an attempted mutiny within their own ranks were now rallying armed resistance to lay siege to the Mechanicum Control Panopticon, which would answer neither Vox-hail or override command, and was the undoubted source of the malign digital broadcast drowning out all others. The frantic provost marshals, unable to make headway against the automated defences which ringed the Panopticon citadel, gave way to the elite white-armoured Veletaris sections of the 905th Lethe Cohort, the "Ash Scorpions" as they had come to be known. Veterans of a dozen ferocious war zones, the discipline of battle had turned these Feral Worlders into a lethally effective fighting force. Blasting through bulkheads with Melta Bombs and tracked Rapier cannon, they worked their way corridor by corridor, cutting down any resistance they met with savage crossfires of Volkite rays and forced a passage through the Maw's labyrinth of tunnels towards the generatora which supplied the Panopticon with its power.

As they battled closer to the Mechanicum section, matters became yet more desperate as the station's fabric itself seemed to turn against them and they were forced to bring up Flamer units to scour the passageways of scuttling haemonculites and darting Servo-skulls, driven in frenzied attacks like maddened animals. Breaching their way at last into the great generator vault, they found a vast cathedral-like space, dominated by five enormous, lightning-shrouded plasma coils, each as large as a Battle Titan. Here stood the acolytes of the treacherous Archmagos-Astral Mercuric, hulking Tech-priests as heavily armoured as Legiones Astartes Terminators in order to endure proximity to the radioactive infernos they tended, metre-wide steel spiders which leered with the rictus-dead grins of human skulls from the gantry-ways and webs of cabling that festooned the vault, and scores of blank-eyed Servitors, their flesh scorched cinder-black. Beyond all these, guarding the central control pulpit, was a maniple of iron-grey Castellax Battle-automata, their Bolt Cannons levelled and cycling; a deadly barrier beyond which nothing could pass.

Veletaris of the 905th Solar Auxilia Cohort, "the Ash Scorpions"

Battle was joined. The fate of Port Maw hung in the balance, bravely the Ash Scorpions advanced into heavy fire, rushing from cover to cover as fast as they could as they tried to find a way through the tangle of consoles and companionways to the heart of the generatora. Soon the cavernous vault was filled with a hurricane of shrieking energy blasts and roaring bolt shells. Machinery exploded, companionways buckled, acrid smoke filled the air. Men and automata were cut down alike, steel claws found flesh and bit deep, Flamers gouted their hot breath, grenades clattered and thundered, shredding bodies and sundering metal. Amid the storm, the wall of Castellax automata stood unbreached, their armour scorched and smoking as blasts and shell washed over them like hail across stone until a trio of tracked Rapier batteries emerged from the smoke, the shearing beams of their Laser Destroyers converging on the lead Castellax and sending it to burning oblivion.

Sensing that their moment had come, the Veletaris storm sections broke from cover, screaming the ancient blood-cries of their Feral World, and charged the breach in the lethal barricade of Battle-automata. Dozens died before they reached it, torn to pieces by the fury of the Mauler Bolt Cannon of the surviving Castellax, while others were pulverised by the heavy blows of their servo-claws, but like a pack of raptors they swarmed the armoured behemoths, Volkites spitting hellish rays at point blank range into joints and tears in the Battle-automatas' armour. Another of the Castellax fell, thrashing in blind rage as its legs were cut from beneath it, and the Veletaris surged through, crashing into the Tech-priests with a strength born of desperation and sacrifice that could not be allowed to be in vain.

Only a single Veletarii Prime, whose name has gone unrecorded, managed to force his way through the tumult and slaughter to the dais of the control pulpit, his Void Armour blood-splattered and aflame. With no time for thought or plan of action, he plunged his Power Sabre directly into the heart of the machine, even as vast steel claws were fastening themselves around his pressure helm. The pulpit dais exploded in a blazing white fireball, murderous arcs of lightning shot from the great plasma reactor cores, ravaging the vault as their emergency protocols engaged, and the misdirected power was vented into the capacitors which lined the wall, burning men and machines caught between them into clouds of cinders.

Outside, the interference signal blanketing Port Maw first faltered and then failed.

Triumph and Betrayal

In the void-space around Port Maw sudden, deafening silence cut through the incessant pulse across the Vox and signal network of the Loyalist voidships and in its wake matters immediately became less chaotic and more murderous as battle lines were swiftly drawn between friend and enemy, hails sent and answered, ultimatums and demands for surrender issued and spurned, and command asserted in the face of the crisis.

Aboard the titanic Triumph of Reason, the Port Maw Armada flagship -- a huge fleet control vessel re-forged from the twin hulls of two Legatus-class macro-battleships crippled in the earliest years of the Great Crusade -- the attempted assassination of Grand Admiral Ospheus LaBray had been thwarted and an attempted mutiny eradicated with bloody certainty. LaBray was now once more in command of the immense warship and with the malign signal countered, the auguries and strategium-luminator systems of the Triumph -- designed to order and direct an entire Segmentum fleet-of-war if needed -- reasserted tactical control over all Loyalist vessels that would answer its call. LaBray's first order was to the Dictatus-class ram-battleship Kurga, which hung in orbit near the Port Maw station, having just similarly suppressed a mutiny of its own. Awakening to war, it powered towards the now silent Mechanicum Panopticon tower, the six-kilometre-long armatures of the ram-battleship's triple servo-claws extended. The Kurga smashed into the tower, the thirty-metre-long teeth-spikes of its claws piercing its armour and sinking slowly through its guttering power fields, and were joined moments later by scores of rocket-fired Melta-barbed harpoons which speared into the brazen faces of the tower. Its victim secured, the Kurga’s drive burned white hot. The ten-kilometre-tall tower shivered and cracked, resisting defiantly against the unimaginable forces tearing at it, but soon shuddered and gave way as the Kurga’s oversized engines burned like hellfire. The tower broke, a myriad of secondary explosions rippling along its length as it crumbled like rotten wood and was dragged free into the void. The malign signal would not sound again.

At the centre of the maelstrom of voidships, Loyalist and Traitor vessels began to break apart, guns firing in fitful bursts, uncertain of friend and enemy. On the outer edges of the vast, slow, vortex of ships, tens of thousands of kilometres from Port Maw itself, the outriders of the great armada were only just recovering. These vessels had not been part of the core fleet at the Maw and comprised dozens of reinforcement squadrons sent to the muster from other systems, along with numerous refugee craft and mass conveyors, around which were small provender and repair vessels that flitted like tiny sea creatures swarming around ocean leviathans. Here, removed from the heart of the treacherous attack, the carnage had been less extreme and the mutinies fewer, but still the anathema signal from Port Maw had blinded and deafened them for a time and now most were bewildered and uncertain of just what the catastrophe unfolding before them meant, uncertain of who was firing on whom, or why.

An Imperial vessel succumbs to traitorous fire

At the outermost edge of the maelstrom of warships, and all but unnoticed in the confusion, one of the great war-arks of Cyclothrathe, which had so far taken neither side in the anarchy, now triggered its manoeuvre jets and came about. The colossal barrel-shaped vessel slowly turned and pointed its prow towards the opposite edge of the spiral arm of outer ships to the still unengaged warships of the Cruiser squadron sent from distant Agathon to answer Port Maw's call. Not one of these vessels bore a Traitor inside and to them the battle yet had no seeming cause and no clear side to choose. The Cyclothrathine war-ark, designated Arithmetic of Violence, silently broke apart, its ten-kilometre-long hull plates separating like the petals of a colossal flower in the storm. Revealed within in place of internal decks were row upon serried row of inert void torpedoes, which, as if lit by a single torch, ignited their plasma drives with a golden blaze of fire. They burned across the void to the Agatheans, smaller ships caught in their path obliterated instantly, and struck home like the obliterating fist of a god. The sudden searing flash of a score of mighty warships dying at once in fire was so bright, that in that instant it burned visible to the naked eye even to the dark edges of the system's Ort-cloud. And there in answer, a gigantic black warship came to life.

The Ravens

At the same hour that the first footfalls of the Titans were sounding at Hive Illum on Manachea, at Port Maw open void battle had now erupted between those ships that had turned fully Traitor and those who had remained Loyal, while all across the artificial planetoid station below them, civil war was being waged with bloody conviction. The Traitors' plan had proved only partly effective in conquering the Loyalist fleet from within or forcing its surrender, and now the malign influence radiating from the Mechanicum Panopticon had been ended, the Loyalists were rapidly gaining strength.

After the bloody and chaotic skirmish, those warships that remained mobile had broken away and parted into two battle lines, forming thousand-kilometre-long crescent formations mirroring each other in orbit round the Maw, each now staying their range and keeping the bulk of the artificial planetoid between them and the enemy as they manoeuvred to form up. Around them hundreds of wrecks and stricken voidships cascaded, reeling with damage or drifting paralysed as bloody struggles raged on within them for control. Neither force had such overwhelming superiority yet that a direct attack on the other would guarantee victory without severe losses, but both knew that to attempt to flee -- to turn away from the enemy and run -- would be to secede the entire strategically vital star system and all it contained to the enemy. The fate of Port Maw and its vast armada hovered on a knife's edge.

As the two battle lines fell into a deadlock, from the darkness of the outer system came a new and unexpected threat. The dark fleet answered no hails, broadcast no identification cyphers, but came hurtling on at near relativistic speeds like a dagger hurled at the heart of Port Maw. In the strategium of the gargantuan Loyalist flagship, the Triumph of Reason, Grand Admiral LaBray awaited impatiently as his sensorium officers strained their Auspexes to get a firm report on the incoming fleet. Some form of masking technology was being employed that scattered and defused the scanning beams, making a definite fix on the vessels impossible to attain. LaBray likely knew, as many of his rank did, of the rumours of such arcane devices being employed by the secretive Raven Guard Legion -- a Space Marine Legion which remained Loyal, but was reported destroyed at Istvaan V.

Could this be a Raven Guard splinter fleet, the survivors of that cataclysmic battle? If so why did they not answer, why did they not identify themselves? These questions could not be readily answered. But however effectively their true nature was shrouded from LaBray's Auspexes, while operating at such intense acceleration, their engines burning bright with plasma thrust, they could not hide their number; there were twenty vessels by their drive flares, at least half of which were capital class by his savants' estimations, meaning LaBray's own fleet outnumbered the interlopers by a margin of four for one. It was a force which alone he could overwhelm, but if it joined with the mass of the enemy now matching him in orbit on the other side of Port Maw, would likely tip the balance in the Traitors' favour. Without hesitation LaBray gave the order, and the vast crescent of his armada turned and began to arc toward the stranger-fleet on an intercept vector, their own engines burning bright.

The distance closed, thousands of kilometres flashing by in mere seconds, and behind the Loyalists the Traitor fleet followed suit, but it would be LaBray's ships that would meet the newcomers first, that was now inevitable. The solar minutes ticked by until it was reported that the incoming ships were now close enough to be within visual range of the flagship's occularis, and LaBray immediately ordered the image up before him. It was only then that he realised the depth of his mistake. The vanguard of the incoming ships were indeed Legiones Astartes Battle Barges of the Raven Guard, or at least had been; two modified Dagon-class Grand Cruisers bearing the sable heraldry of the Primarch Corax's Legion now torn and burned in the fires of battle, but what came after them was not of the Raven Guard. The monster rose up behind the Battle Barges, making them seem as mere frigates in comparison to its nightmare magnitude. It was a ship no Imperial captain could ever have failed to recognise at first glance, it was a war machine few vessels could ever hope to match, but what its presence portended was darker still. It was the Vengeful Spirit; it was the flagship of Horus.


Pre-Heresy pic-capture of the Sons of Horus flagship, the Vengeful Spirit

The warships of the Sons of Horus cut into the Loyalist battle line at its apex, smashing into it head on, the turncoat warships of the Raven Guard being sacrificed to soak up the fury of the Loyalist guns as they closed. The Traitor spearhead of warships cut into the Loyalist fleet like a lance, piercing it bodily, splitting the Loyalists' defensive formation in two like an axe cleaving meat.

At the apex of the spearhead, the Vengeful Spirit came on through the blast waves of flames and debris ahead of it like a beast of ancient myth made real, its armoured prow smashing aside Loyalist cruisers like toys, its many-decked broadside batteries smashing shields and cracking open hulls with contemptuous ease as it passed. Along its darkly armoured flanks, strange symbols writ as if by a colossal hand seemed to flicker and fade, as if pulsing to some terrible heartbeat and the void around it appeared to twist and recoil. The juggernaut-ship plunged on through the Loyalist vessels, dealing death as it went, unstoppable. The gargantuan Battle Barge of Horus had one goal, one true target; the Triumph of Reason protected at the heart of the Loyalist armada, and the focus of its command and control.

Its quarry in sight, the Vengeful Spirit made as if to ram the vast double-hulled Triumph of Reason, but as it closed -- the guns of both hunter and prey blazing savagely -- the Vengeful Spirit’s engines flared and it spun suddenly on its axis -- a manoeuvre which at that velocity should have been fatal for any ship of its size -- the manic and unexpected turn smashing to dust two hapless Escorts that found themselves in its path, while a bastion frigate that caught the full blast of the Vengeful Spirit’s engines as it swung was flung burning into the void. The space between the two gargantuan warships seemed to distort and shudder as the ship of the Warmaster violently arrested its progress so that it now flew above and alongside the Triumph -- matching her course and velocity. In response to the seemingly impossible manoeuvre and the threat now looming vulture-like over the Triumph, the lumbering giant below her tried to throw herself aside to evade what was to happen next or at least try to bring her own broadside to bear, but she was too slow and it was too late. Vortex missiles, rare and deadly weapons of the Dark Age of Technology, spat from the Vengeful Spirit’s broadside launch tubes and exploded in ghostly spheres of silent nothingness that tore away the Triumph of Reason’s Void Shields like paper and cracked open the decametres-thick hull plating beneath them like splintering ice. Seconds later, the Dreadclaws and Kharybdis of the Sons of Horus followed, punching through the weakened hull in a score of places and spilling out a cargo of death within. Gunships and assault rams followed, forcing their way into flight bays and hangars, crash-landing in a storm of fire and shell.

Throughout the Triumph emergency alarms sounded "repel boarders", security bulkheads slammed shut and weapons cages were flung open to arm the thousands of crew, from the lowliest galleys rating to the highest astrogator. The elite Solar Auxilia of LaBray's own Lifeguard Cohort rallied to meet an invader that was already within their iron walls, and soon corridors and gun decks were filled with the din of battle and the screams of the dying. Quickly, the Sons of Horus assault forces smashed their way into the core of the vast and labyrinthine double-hulled warship, killing with controlled savagery, viridian-hued Legion Breachers locking shields to march down on automated gun stations that turned the air in front of them into hurricanes of shellfire, heedless of their punishing losses. Elsewhere, Sons of Horus Reavers turned crew decks into blasted abattoirs, headless bodies strewn in their wake as crew, Servitor and armsmen alike were slain without mercy by Bolter and blade.

At defensive chokepoints and at the gateways to vital compartments, the Solar Auxilia Lifeguard made their stand as black armoured Terminators thundered inexorably towards them, maintaining disciplined volleys of las-fire of such intensity that the sable ceramite of the Cataphractii began to glow a dull ember red and their gilded chasements ran molten as hot wax. In the bowels of the Triumph, armoured locking mechanisms were thrown open, cryo-chambers vented and at LaBray's command the last line of his gargantuan flagship's defence was set loose upon the enemy; Ogryn Charonites - hundreds of them. Mutilated, cybernetically-augmented monsters, fueled by rage and combat stimulants -- barely controllable -- the process that created these beasts of war were themselves based on techno-arcana many had thought better abandoned to the Age of Strife. But such creatures were still maintained under Imperial dispensation to the masters of the Solar Auxilia, a weapon of dire resort that was unleashed now against the Sons of Horus. The hulking, surgically-armoured Abhumans towered over a Space Marine, and their augmetic fists could crush Power Armour as easily as bulkhead plate.

Even against the superhuman warriors of the Sons of Horus, in the confines of the Triumph’s passageways and engine decks, the Charonites proved deadly, smashing into their ranks and sending them flying or ripping them apart like over-cooked meat. Bolters hammered the Charonites at point-blank range, blowing out bloody chunks of their chem-infused flesh, Chainswords slashed and wheeled, but to seemingly no effect, and the insane Abhumans ploughed on, heedless of the wounds that would have killed even a Legiones Astartes many times over -- even headless they sometimes continued to murderously flail around them until life was torn from bodies smashed beyond recognition. Force was met with force, savagery with savagery, and soon the Traitors' attack began to stall as casualties mounted on both sides. For the briefest moment, a glimmer of hope came to the embattled survivors of the Triumph of Reason, only to die as the eerie screams of reality being torn open echoed all across the Loyalist flagship as the Vengeful Spirit’s second wave of attack teleported on board, and with them came Horus.

Horus, the Warmaster, Primarch, God of Battle; nothing could stand before him. Into the thickest concentration of Charonites he charged, his black-pelted cloak streaming behind him, his maul, Worldbreaker, crushing the Ogryns as if they were inert figures of gore-filled porcelain rather than the nightmares of Old Night made flesh. In him his Legion found new vigour, a dark power seeping into their souls which hurled them at the enemy once more like the devils of ancient lore. Seeing that all was lost, LaBray led the last of his personal Lifeguard in an attempted break for the ship's fighter bays, hoping no doubt to escape to another Loyalist vessel, but even in sight of the launch bays they were cut off. Denied even the glory of a last stand, LaBray and his party were torn apart in a savage crossfire, his half-incinerated body only later identified long after Warmaster Horus had moved on from the war ravaged star system. As a tide of murder, Horus and his sons crashed through the Triumph of Reason, obliterating all in their path, until at last, the command decks were breached and the Strategium broken open, and all within slaughtered without deference to rank or title. Before Horus, the human crew of the Triumph of Reason simply cast down their weapons in despair, but such submission did not save them. From the corpse-strewn bridge of the Loyalist flagship, the Warmaster addressed the surviving Loyalist fleet, his voice burning across the cold void to the very depths of Port Maw where the fighting raged on still. To those who resisted him, this god of death offered mercy and praise of their valiant, if deluded, struggle: submission and service to him would spare them, only this. They would be his now and forever, or they would be exterminated utterly.

Leaderless, broken, and alone the Loyalists were now confronted with the same unimaginable force that had cowed and butchered countless star systems in the name of the Emperor, and had no answer to its inhuman power. One by one, save for a handful such as the Kurga who fled into the darkness, the Loyalist ships struck their flags, dispersing their shields and cutting their targeting Auspexes and thereby surrendered. Within the myriad corridors and vaults of the great station complex itself, the din of battle died away to a dreadful silence, broken only by the cries of the wounded and the dying.

Port Maw and everything in it now belonged to Horus Lupercal.


The conquest of Port Maw opened the way for the progress of the Warmaster's hosts, beginning what would later be called the March on Terra, a succession of campaigns and conquests that would see the Traitors creep ever closer to the Segmentum Solar and the Imperial Palace on Terra itself. Horus and his Legion would not stay long on Port Maw or indeed the Manachean Commonwealth as the frontline still needed to move further, soon reaching shunned Gyrién, storied Dwell and even the vaunted Fortress World of Molech whose defences stood even greater than those of Manachea. All would be conquered and fall before the Traitors' implacable advance.

The outcomes and repercussions of the Treachery at Port Maw were many. First and foremost, the fall of the Manachean Commonwealth and Port Maw marked the foundation of a true secessionist empire, an almost functional Traitor-held domain that had been carved out from the flesh of the Imperium. It would be on Port Maw and not on Manachea that Horus would establish this new domain, given the stricken and blood-bedecked Triumph of Reason over to Taloc Thorne, a former line Captain of the Sons of Horus and the newly proclaimed Tyrant of Port Maw who was given power and authority over this new realm, to rule it and defend it in the name of Horus. Renaming the mighty vessel The Lash, the former flagship became a sombre, blood-bedecked throne room for its new ruler. Given troops drawn from those Solar Auxilia Cohorts recruited on the Sons of Horus' own homeworld of Cthonia -- six full cohorts of Chtonian Jackals -- and an entire battle company of Astartes, this new ruler would impose a Dark Compliance on both Port Maw and the worlds of the former Manachean Commonwealth. With the conquest of Port Maw, the Traitors gained a strong naval stronghold and perhaps most importantly, the necessary facilities to rearm, reequip and repair their war-weary or stricken warships for the long and undoubtedly punishing push to Terra. Within a few short solar days, envoys of the Dark Mechanicum -- to whom the anchorage points and ship-fanes had been given over -- had reconstituted the Maw's operational capabilities; with the damaged Sons of Horus Strike Cruiser Oblivion -- which had been damaged during the final assault on Hive Illum -- believed to be one of the very first vessels to be repaired there.

Secondly, the corruption of much of the troops and vessels of the Port Maw Excertus had considerably added to the Traitors' ranks, most notoriously in naval might where it was estimated that more than a hundred vessels had rallied or been forced into the service of the Warmaster. Of these mighty vessels and troops Port Maw was quickly stripped -- deemed secured -- to fight in other campaigns or foreign star systems as the civil war spread through the Imperium. Yet, for all the advantages it had brought -- including the ultimate death of Grand Admiral Labray and the capture of his flagship -- the Treachery was not a total victory for the Traitors.

On many occasions, the turncoat elements of the Imperium's military branches had been kept in check despite benefitting from an overwhelming element of surprise. Even though having suffered few casualties and even added to its ranks, the Traitors were now far more fractious than they had been before. With many of the turncoat vessels and troops despatched to fight on other fronts -- perhaps as a result of Horus' lack of trust regarding their true allegiance -- Port Maw was now left far more vulnerable than it had ever been before, Horus leaving but a skeleton fleet of perhaps seventy vessels of the line behind him to impose order and the bloody quotas he demanded from the worlds he had conquered. Whilst this fleet was more than enough to keep the Dark Compliance within the Port Maw and Manachea Systems, they proved desperately too few to truly control the vast expanses of the Coronid Deeps. With so few vessels and troops at his disposal, Taloc Thorn could also exert little authority over those independent factions that had allied themselves with the Warmaster and that began pursuing their own agendas almost as soon as Horus had left rather than to follow his orders. Most notoriously amongst these was the Cyclothrathine Mechanicum which shunned the duty to protect and man Port Maw as much as it dared in regard to pursue its own war of conquest in the Coronid Reach with the conquest of the Agri-world of Numinal or the colonies of the Cerada Trinity, whilst the reaver-Knights of House Ærthegn led their own raids in the Grail Abyss.

The successful escape of a single Loyalist Cruiser -- the Telemachus -- and its return to the Agathean Domain would also have dire consequences for the Traitors, spurring the retired hero of the 60th Expeditionary Fleet, Ireton MaSade, into action. Seizing power from the weakening grip of its planetary rulers, Ireton MaSade would put the entire star-system on a war footing, pursuing a war of vengeance against the Cyclothrathine Mechanicum he considered solely responsible for the death of his beloved grandaughter -- the Telemachus’s captain, Jocasta MaSade. This course of action, which would ultimately lead to the famed Liberation of Numinal and open a secondary front behind the main lines of the Traitor's advance, funneling important resources and troops and further destabilising the entire region.

Notable Vessels

  • Triumph of Reason (Unique Battleship, Unknown Class) - The Triumph of Reason was a vessel with a long and twisted history. Built from the wrecked hulls of two prior Legatus-class Battleships that had been mauled early on during the Great Crusade, the Triumph of Reason was easily the biggest ship in the entire Segmentum Obscurus Armada. Rebuilt after a unique pattern, the Triumph of Reason was designed from the start to become the flagship of the entire Segmentum Armada and much weight and space was given over to communication and Auspex devices. Stationed at Port Maw for the greater part of its career, placed under the command of Grand Admiral Ospeus LaBray for much of its early years, the Triumph of Reason was equipped with countless cryo-chambers to harbour Ogryn Charonites, the only troops at the admiral's disposal that would prove superior to traitorous Legiones Astartes in case of boarding actions. The Triumph of Reason would participate in the early hours of the Horus Heresy at the notable Treachery at Port Maw where it would assume control and command of the entire Port Maw Armada and its allies once the destruction of the Mechanicum Panopticon at the heart of the treachery had been confirmed. It would be from the bridge of the Triumph that Grand Admiral LaBray would coordinate the battle against the Sons of Horus fleet, even engaging the infamous Vengeful Spirit of the Warmaster Horus himself. Outmanoeuvred by the Vengeful Spirit, the Triumph of Reason came under attack by Sons of Horus boarding parties and even the Archtraitor Horus Lupercal himself after the first assault wave had been nearly thrown back by the hundreds of Charonites held in the Triumph's bowels. Seized from within and with LaBray being killed in his failed attempt to abandon ship, the Triumph of Reason would remain at Port Maw for the following years of the civil war, its communications hub needed to replace the destroyed Panopticon. The once-proud Imperial vessel became a glorified if macabre throne room for Horus' chosen regent, a Sons of Horus line Captain by the name of Taloc Thorne, who renamed the battleship "The Lash" and took the title of the Tyrant of Port Maw.
  • Vengeful Spirit (Gloriana-class Battleship) - The Vengeful Spirit was a towering Gloriana-class Battleship modified to confirm to the Scylla Pattern and that served faithfully as the Luna Wolves' -- and later the Sons of Horus' -- flagship during the entire Great Crusade. As flagship of the XVI Legion, the Vengeful Spirit was also the personal warship of the Warmaster Horus Lupercal, harbouring his command centre and throne room, its hull being adorned by the Warmaster's own emblem; the Eye of Horus. More powerfully armed than nearly any vessel in service of the Emperor, the Vengeful Spirit would become a dreaded sight during the dark years of the Horus Heresy, preying on Imperial star systems with its powerful engines which made the colossal battleship a far quicker predator than most readily believed. By the time of the Manachean War, the Vengeful Spirit’s transition to a flying temple to the Dark Gods had already begun, its once proud hull defaced with ritual and esoteric symbols several hundred feet wide and in all likelihood painted with human blood. Present at the events known as the Treachery at Port Maw, the Vengeful Spirit would lead the Sons of Horus into the developing battle between Traitors and Loyalists of the Port Maw Armada. Approaching covertly behind two captured Raven Guard Battle Barges, the Vengeful Spirit would almost immediately head for the Triumph of Reason, the Loyalist flagship which it badly mauled before sending boarding parties to capture the pride of the Port Maw Armada. The Warmaster himself would be forced by necessity to join the boarding actions, as his troops were being slowly overwhelmed by rampaging Ogryn Charonites Grand Admiral LaBray had released as a last line of defence. Turning the course of the battle by himself, Horus was however denied the satisfaction of slaying the Grand Admiral. The Vengeful Spirit would leave the Port Maw System carrying the Warmaster all his way to the Battle of Terra and his final confrontation with the Emperor of Mankind. The Vengeful Spirit still roams the galaxy, having found refuge in the Eye of Terror with the Black Legion of Abaddon the Despoiler.
  • Arithmetic of Violence (Mechanicum War-ark, Unknown Class) - A gigantic vessel of nearly ten kilometres in length, the Arithmetic of Violence was only one of a trio of such vessels present at Port Maw during the events of the Treachery. Secretly in league with Horus for many years, the Cyclothratine Mechanicum had infiltrated the Port Maw muster under the guise of loyal servants of the Emperor. When the blanketing signal was released from the Mechanicum Panopticon Tower, the Arithmetic of Violence used the surrounding pandemonium to manoeuvre itself into perfect launch position for its devastating complement of plasma-torpedoes. Blossoming like an unholy flower, the Arithmetic of Violence shed her long hull plates and revealed row upon row of void torpedoes that annihilated the allied fleets of Agathon, Numinal and the Cerada Trinity in a single devastating volley -- for their crews and captains had not been corrupted or infiltrated and remained staunch Loyalists of the Emperor. Yet the Arithmetic of Violence failed in its task as one lone survivor -- the Telemachus -- remained and would escape from the system to carry news of this betrayal to its homeworld.
  • Kurga (Dictatus-Class Battleship) - The Dictatus-class was an ancient class of ram-battleship that had slowly become obsolete as the Great Crusade wrought on. The Dictatus-class were almost primitively barbaric in their design as their main role was to ram enemy voidships and shred their hulls like an ancient seaborne predator with their enormous jaws -- a tactic that seems more suitable for the dreaded Orks than the Emperor's soldiery. Mounted on a set of hydraulic platforms, these triple gigantic servo-claws -- each one of them nearly six kilometres in length -- comprised a row of nearly thirty-metre-long teeth-spikes, while its "mouth" supported scores of rocket-powered Melta-barbed harpoons not unlike the more massive Ursus Claw that was the pride of the World Eaters flagship, the Conqueror. The Kurga was present at the Treachery of Port Maw from which it remained one of the few Imperial warships that succeeded in making good its escape despite having to crush a mutiny on board. It remains famous to this day for having shred and ripped off the Mechanicum Panopticon tower which Traitor elements had used to sabotage the Armada's communication network and targeting arrays. The Kurga would go on to fight with distinction in the years after the Treachery, its powerful drives and unorthodox tactics proving a valuable asset in the dark years to come.
  • Telemachus (Unknown Class, Cruiser) - The Telemachus and her sister-ships -- all veterans of the former 60th Expeditionary Fleet -- answered Grand Admiral Ospeus LaBray 's call after the costly destruction of the Space Hulk known as the Red Polyphemus. Battlefleet Agathon send an entire squadron of Cruisers to the gathering Imperial armada at Port Maw. The Telemachus ' captain was none other than Jocasta MaSade, grandaughter of the famed Ireton MaSade, former Imperial Commander of the Agathean Domain and future hero of the Imperium. The Telemachus was the sole survivor of the eight Agathean Cruisers send to the great Armada Imperialis muster at Port Maw, its sister-ships all falling prey to the treacherous attack of the Arithmetic of Violence during the infamous Treachery at Port Maw-incident. This single act of violence would trigger a gruesome war of vengeance between the forces of the Agathean Domain and those of Forge World Cyclothrathe. Despite her wounds, the tenacious Jocasta MaSade refused to leave her bridge, urging her crew to fight on. It was only once the Telemachus had escaped the trap set for her that Jocasta MaSade let herself be examined. Alas, by then the damage had been done and the valiant captain died from blood-loss. The arduous journey back home would however set events in motion that determined the Agathean Domain's participation in the Horus Heresy.


  • The Horus Heresy - Book Four: Conquest by Alan Bligh (Forge World Series), pp. 10-11, 36-54, 72-73, 86-89, 189

Battles of the Horus Heresy
004-006.M31 Battle of ProsperoIstvaan III AtrocityWar 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 VannaheimSecond Battle of ParamarBattle 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 CampaignLiberation of NuminalBattle of ArissakBattle of PerditusBattle of SothaScouring of Gilden's StarBattle of NyrconBattle of TallarnBattle of NocturneBattle of Pluto
011-014.M31 Malagant ConflictBattle of the Kalium GateBattle of CatallusBattle of TralsakTarren SuppressionBalthor Sigma InterventionScouring of the Ollanz ClusterBattle of ZepathBattle of AnuariBattle of PyrrhanSecond Battle of DavinBattle 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-GarmonDefence of RyzaBattle of ThagriaSolar WarRaid on LunaSiege of TerraGreat Scouring