Horus Heresy Chronology - Prelude to Heresy: Below is a chronology of the events immediately preceding the start of the interstellar civil war later called the Horus Heresy. Though the Warmaster Horus turned to the service of Chaos several standard years before the start of the conflict, the Heresy only officially began with the Isstvan III Atrocity as Horus' duplicity was not yet revealed.003.M31 Contact Lost with the Isstvan System - Six Terran years after the last official communiqué from Isstvan III, a Death Guard patrol ship on the outer edge of the XIVth Legion's fleet picked up an incomplete astrotelepathic transmission which indicated that Isstvan III was in open religious rebellion against the Imperium. The Imperial planetary government had collapsed, and the Planetary Governor Vardus Praal, now a turncoat and perhaps become a mutant or psyker, was leading the revolt.004.M31 Davin Plague Moon Campaign and the Fall of Horus - The Warmaster Horus is grievously wounded while fighting Chaos-corrupted rebels led by Eugen Temba on the Plague Moon of the Feral World of Davin when Temba wields the Nurglish weapon known as the Anathame against him. He is healed within the ancient Temple of the Serpent Lodge on the moon but though his life is saved, his soul is forfeit to the Ruinous Powers by his own choice. From this day forth he makes his plans to bring the Imperium to ruin and topple the Emperor from power. Though his treachery and malign intent remain hidden, he begins his far-reaching conspiracy to suborn those of his brother primarchs' Space Marine Legions and the other military forces of the Imperium who will aid him and neutralise the threat of those who will not serve him where he can. He prepares in secret over the next two Terran years to fight a sudden and ruthless galactic civil war.004-009.M31 Signus Cluster Campaign - The bulk of the Blood Angels Legion is dispatched through the machinations of the Warmaster Horus to the distant Signus Cluster to put down a local uprising. In the Signus Cluster the Blood Angels discover worlds scoured of all life by an unknown enemy. Knowing the IXth Legion will never join his cause and fearing their Primarch Sanguinius, Horuss had set his trap with the aid of his allies in the Warp at Signus Prime, where the Blood Angels are beset by a foe none have ever faced before, the daemonic legions of the Ruinous Powers and assailed by terrifying psychic assaults and distortions of reality. Trapped on Signus Prime, the Blood Angels are ambushed by a horde of Chaos Daemons, facing horrific casualties until their primarch defeats the murderous Bloodthirster Ka'bandha in single combat.004.M31 Destruction of Olympia - While the Iron Warriors Legion was cleansing the world of Gugann of a major infiltration of the infamous xenoform known as the Hrud, the long-lived Satrap of Olympia died. With the death of the Tyrant of Lochos, the Iron Warriors' homeworld of Olympia erupted into infighting and insurrection. The population had taken up arms against the Imperium following many solar years of relentless anti-Imperial propaganda by the dead Tyrant. Tired of repeatedly having to prove himself, and enraged at the disregard of his fellow Legiones Astartes who have left his Legion to carry out dishonourable work as garrison forces, the Primarch Perturabo and the Iron Warriors brutally suppressed the rebellion on the streets of the city-states of Olympia. No one was spared. It was the principle of surrender or no quarter, and the Iron Warriors had grown accustomed to granting no quarter. Perturabo watched as the Olympian fortifications in which he had once taken such pride were overcome. By the time the massacre was over, Olympia had been culled into slavery. Five million civilians had been killed in the process. Horrified at what he had done in his rage, Perturabo knows the Emperor will never forgive him. But Horus offers him another path...004.M31 Destruction of the Auretian Technocracy - The already corrupt Horus assassinates the Auretian Technocracy's leader, the Fabricator Consul, who represented that independent Human government, in order to obtain highly-coveted lost Standard Template Construct data. Horus later uses this illicitly recovered STC database to entice Fabricator-General Kelbor-Hal of the Mechanicum to join the Traitor cause. This plants the seeds of the Dark Mechanicum's birth and the eventual Schism of Mars.004.M31 Battle of Tarsus -The Primarch Fulgrim meets with the renowned Aeldari Farseer Eldrad Ulthran of Craftworld Ulthwé on the Maiden World of Tarsus, in which the Farseer attempted to warn Fulgrim of the Warmaster Horus' corruption by Chaos. Ultrhan explains that Horus has been fallen to the Dark Gods after being wounded by a malefic Chaos blade known as the Kinebrach Anathame at the hands of the Traitor Eugen Temba upon Davin's Nurgle-corrupted moon. Fulgrim reacted with violent outrage at the Farseer's accusations due to his close kinship with his brother Horus. This outrage was further enhanced by the corrupting influence of Fulgrim's daemon-possessed Blade of the Laer, which darkly influenced the Primarch to reject the Aeldari's truth and provoked Fulgrim into launching an unprovoked and furious attack on Eldrad and his retinue alongside his Emperor's Children Captains and his personal Phoenix Guard. In the battle that ensued, the Emperor's Children slew both the revered Aeldari Wraithlord Khiraen Goldhelm and a potent Avatar of Khaine, which forced the Farseer and the other Aeldari troops to sorrowfully withdraw, as they realised that Chaos had already claimed yet another of the Mon-Keigh's Primarchs. Yet they succeeded in killing all of Fulgrim's elite personal Phoenix Guard before their departure. Believing the Aeldari had proven themselves a treacherous xenos race that sought to divide and conquer the Imperium by spreading such lies about its leaders, Fulgrim, again under the increasing influence of the Laer daemonblade, ordered the destruction of several other beautiful Aeldari Maiden Worlds using hideous Virus Bombs.ca. 004.M31 Battle of Deep Orbital DS191 - Following his delegation to the 63rd Expeditionary Fleet, Fulgrim announced to his senior commanders that he would lead a small force to join his brother Primarch Ferrus Manus and his Iron Hands at Callinedes IV in the Callinedes System under the pretense of clearing it of an Ork infestation. The Emperor's Children Primarch spearheaded the assault during the pacification of Deep Orbital DS191, leading the 1st, 2nd and 3rd Companies. During the assault, Captain Solomon Demeter, commander of the Emperor's Children's 2nd Company, found himself unsupported by the 1st and 3rd Companies as the battle-plan had laid out. Overextended and in real danger of being cut off and destroyed, the 2nd Company was only saved from certain destruction by the unplanned and timely arrival of the 10th and 13th Companies under the commands of Captains Saul Tarvitz and Lucius, two junior officers that Demeter had found himself associating more and more with as he was systematically frozen out by the III Legion's high command. A dark shroud hung over Lord Commander Vespasian after witnessing these dishonourable actions. He felt obliged to act after he observed Solomon Demeter's 2nd Company being intentionally abandoned by both Captain Kaesoron's and Vairosean's companies. It was a decision that would cost the honourable Astartes his life when he was murdered by the Chaos-corrupted Fulgrim himself.004-005.M31 Start of the War in the Webway - Learning of Horus' treachery and agreement with the Chaos Gods to initiate a rebellion against the Emperor through the use of forbidden sorcery, Magnus the Red attempts to warn the Emperor on Terra via psychic projection. In the process, he breaches the wards around the Great Work -- a conduit built by the Emperor and the adepts of the Mechanicum from the dungeons of the Imperial Palace into an extradimensional xenos network once governed by the Aeldari called the Webway. The Daemons of Chaos flood into the Imperial extension into the Webway from the Warp, forcing the Legio Custodes and Sisters of Silence into a solar-decade-long war to protect the heart of Terra itself.ca. 004.M31 Vulpa Straits Hrud Migration - Commanding the 51st Expeditionary Fleet, the Warsmith Barabas Dantioch led a large Iron Warriors contingent against a massive xenos incursion known as the Vulpa Straits Hrud Migration. Upon the Fortress World of Gholgis the Hrud infiltrated and destroyed the Iron Warriors garrison. The intense entropic fields generated by the migratory Hrud swarms caused stone to age and brought flesh to ruin, turning the Astartes warriors into so much dust and bones, rusting their armour and jamming their bolters as the Iron Warriors' fortress crumbled all about them. Only then did the rachidian beasts creep out of every nook and crevice to attack, stabbing and slicing with their venomous claws. This left Warsmith Dantioch prematurely aged and crippled. Very few survivors made it out alive as Stormbirds extracted the survivors from the remains of Gholgis. Many of the Astartes died from premature aging or were left in aged, superhuman bodies. In the Hrud Migration's aftermath, the worlds of Krak Fiorina, Stratopolae and Gholghis were lost. The Warsmith questioned Primarch Perturabo's prosecution of the Hrud extermination campaign, which left half a Grand Company dead. Dantioch soon found himself relieved from command of the 51st Expeditionary Fleet and permanently garrisoned to the world of Lesser Damantyne for his presumption.ca. 004.M31 Cleansing of Arigatta - This was an Imperial Compliance action that was carried out jointly by the Sons of Horus, Ultramarines and the World Eaters Legions against the world of Ariggata. When Imperial envoys arrived bearing word of the Emperor and the Imperial Truth, they were executed in a bloody gesture of independence. Most of the planet was quickly conquered, except for the massive fortress within which most of the leaders of the planet cowered. Eager to be on his way, Horus commanded Angron, primarch of the World Eaters, to take the citadel and kill only the leaders. Eagerly, Angron led the assault. However, the fortress was heavily defended and the casualties were horrendous, a dozen World Eaters falling for every metre of land. Eventually, a ramp of corpses led up to a single breach in the wall, and the Astartes of the World Eaters Legion plunged in and slaughtered all remaining survivors, transforming the fortress into an abattoir of blood. Before Guilliman was able to confront his brother primarchs regarding the massacre on Ariggata, the Horus Heresy erupted, both Horus and Angron spitting on their oaths of loyalty to the Emperor, and Guilliman's worst fears were confirmed.734.004.M31 Burning of Prospero (Battle of Prospero) - Magnus the Red, primarch of the Thousand Sons Legion, learned of his brother Horus' fall to Chaos and attempted to warn his father the Emperor using psychic arts forbidden by the edicts of the Council of Nikaea. His psychic transmission inadvertently unmakes the psychic wards of his father's attempt to create an Imperial extension to the Aeldari Webway. The Emperor was secretly building this extension, the so-called "Great Work", deep beneath the Imperial Palace on Terra with the aid of the Golden Throne and the Mechanicum. With the wards collapsed, daemons begin to flood into the corridors of the Imperial Webway and the Emperor is forced to remain on the Golden Throne to prevent the breach from spilling into the Imperial Palace itself. The Space Wolves, Sisters of Silence and a detachment of the Legio Custodes are ordered to form a Retribution Fleet and bring Magnus to Terra from Prospero in chains to answer for his violation of the Edicts of Nikaea forbidding him from using sorcery. Seeing an opportunity, the Warmaster Horus intervenes and convinces his brother Leman Russ that Magnus' crime is so dire that his life is forfeit and Magnus should never set foot upon Terra alive. The Space Wolves assault the Thousand Sons' homeworld and raze its capital city of Tizca to ashes. While Magnus escapes deep into the Warp through a rift in reality opened with the aid of the Chaos God Tzeentch, the Changer of Ways, his Legion is reduced to but a thousand warriors. Bitter at his treatment by the Emperor, Magnus schemes to join Horus' rebellion.005-014.M31 Schism of Mars (Martian Civil War) - Fabricator-General of the Mechanicum Kelbor-Hal turns against the Imperium and plunges Mars into civil war, those loyal to Terra and the Emperor as the Omnissiah are forced to abandon the Red Planet. Led by the Legio Mortis ("Death's Heads"), the Traitor Mechanicum scoured the surface of the Red Planet of those still loyal to Terra, plunging the first and most important Forge World of Mankind into a bitter civil war that saw the extinction of several ancient Collegia Titanica Legios and dozens of Knight houses. The last to fall were the Loyalist hold-outs of the Legio Tempestus ("Stormlords"), who, perhaps mercifully, died unaware that the bulk of their Legio off-planet had renounced their oaths to the Emperor and declared for the Warmaster Horus. Elsewhere, the Schism of Mars sunders the feudal order of the ancient Mechanicum and its bonds with the Imperium. Many Forge Worlds side with the Traitors, others with the Emperor and still others declare independence from either side. So likewise are the Mechanicum's Titan Legions, the Skitarii Legions and the powerful Forge World Taghmata riven with division. Neither side is able to claim victory for the duration of the Horus Heresy, and Imperial Fists saboteurs fight to disrupt the Traitors' industrial capabilities until the final days of the war. The Traitors of the Mechanicum are soon known as the "Dark Mechanicum."004-007.M31 Purgation of Arkenath - An Ultramarines contingent comprised of five-hundred Legionaries participate in a three-year long campaign against the Vektate xenos overmind, to free the Human population of Arkenath.005.M31 Jorgall Execution - The Jorgall campaign was carried out during the Great Crusade against a xenos race of humanoid aliens known as the Jorgall. Many of these xenos featured extensive cybernetic physical enhancements to improve their physical forms and enhance their fighting abilities. Elements of the Sisters of Silence, alongside the 1st, 2nd and 7th Great Companies with Mortarion as the commander, launched an assault into the main Jorgall cylinder world. penetrated the drive cluster and took out the control of the cylinder world's motive power centre. Battle-Captain Nathaniel Garro, alongside an elite cadre from the Sisters of Silence, neutralised the construct's hatcheries. Following their hard-fought victory, there were dissenting voices from the Mechanicum contingent who petitioned Mortarion for a few days in which to loot the alien craft of technology. The primarch, as was his prerogative, refused the request, as the letter of Malcador the Sigillite's orders -- and therefore, by extension, those of the Emperor Himself -- was that the Jorgall incursion into the sector was to be exterminated and nothing more.005.M31 Battle of Isstvan Extremis - The elite 1st Company of the Emperor's Children Legion fought in concert with the Death Guard Legion's 7th Battle Company under the command of Battle-Captain Nathaniel Garro, against traitorous forces on Isstvan Extremis, the outermost planet within the Isstvan System. Whilst fighting against a powerful Slaaneshi psyker known as a Warsinger, Garro sustained serious injuries; crushing damage to his torso and arm as well as the loss of his right leg from the mid-thigh down. He was only saved from certain death by the timely ministrations of the Emperor's Children Legion's Chief Apothecary Fabius. Taking stock of the desperate situation, the Emperor's Children Lord Commander Eidolon made use of a hitherto unknown ability -- a modified tracheal implant bonded with the Lord Commander's vocal chords that allowed him to produce a nerve-paralysing shriek similar to that employed by certain warrior breeds of the xenos Laer. This powerful ability killed the Warsinger and helped the Astartes carry the day.