Pyre Guard - Horus Heresy: The Pyre Guard's role during the Horus Heresy is not well known to Imperial scholars; what is for certain is that the XVIIIth Legion, along with the Iron Hands and the Raven Guard, were part of the first wave of Loyalist attackers during the Drop Site Massacre on Istvaan V. After the announcement of the Warmaster Horus' treachery against the Emperor and the destruction of the four open Traitor Legions' (the Sons of Horus, Emperor's Children, Death Guard and the World Eaters) remaining Loyalists during the Battle of Istvaan III, the Emperor ordered seven full Legions of Space Marines to attack the Forces of Chaos serving his beloved son and former friend. But amongst those seven Legions, four were already secretly Traitors to the Imperium and devotees of the Ruinous Powers.Following the initial Loyalist assault, it appeared that Horus' forces were soundly beaten, as they attempted a fighting withdrawal from the field. Both the Raven Guard and the Salamanders withdrew towards their drop site to give their recently arrived reinforcements a chance to earn glory against the Traitors. Vulkan and his brother Corax tried to persuade their fiery-tempered brother Ferrus Manus to do the same. But the Gorgon would not be dissuaded from his task. The scent of blood was in the air, and so, the Iron Hands pressed the attack against the retreating Traitor forces. Unknown to the Loyalists, the drop site had been fortified by the four secret Traitor Legions, who had been intended to form the second wave of the Imperial assault on Horus' forces. While the retreat of Horus' rebels was ragged and disorganised, the warriors of the XVIIIth and XIXth Legions fell back in good order. Tanks returned to column, rumbling slowly but steadily back down the slope. The scorched trenches emptied as legionaries filed out in vast hosts, company banners still flying. They were battered but resolute. The dead and injured came with them, dragged or borne aloft by their still standing brothers. It was a great exodus, the black and green ocean of war retreating with the tide to leave the flotsam of their slain enemy behind it.On the northern side of the Urgall Depression, a fresh sea made ready to sweep in and carry all of the mortal debris away. Across from the muster field of the Salamanders, which was little more than a laager of dropships, were the Iron Warriors. Armoured in steel-grey with black-and-yellow chevrons, the IV Legion looked stark and stern. They had erected a barricade, the armoured bastions of their own landing craft alloyed together, to bolster the northern face of the slope. Great cannons were raised aloft behind it, their snouts pointing to the ash-smothered sky. A line of battle tanks sat in front, bearing the grim icon of a metal-helmeted skull. And in front of that, Iron Warriors arrayed in their cohorts, thousands strong. They held their silence and their weapons across their bodies, with no more life than automatons. Not a single Legionary about the XVIIIth stood idle. Yet the Iron Warriors, the entire muster on the northern slope, neither spoke nor moved beyond what was necessary to assemble.Not one responded to the Salamanders' hails. Only the wind kicking at their banners gave any sense of animus to the IV Legion throng. Only when Vulkan started in the direction of his brother, Perturabo, the Lord of Iron returned the Lord of Drakes' gimlet gaze with one of his own. It was only at that moment that Vulkan realised that they had been betrayed. More than ten thousand guns answered, the weapons of their allies turned on the Salamanders with traitorous intent, crushing the Loyalists between the hammer of Horus' forces and the anvil of the fortified drop site. Wrath drove Vulkan up the side of the hill, that and a sense of injustice. The ignoble actions of his brother primarchs had wounded Vulkan to the core, far deeper and more debilitating than any blade. Vaunted warriors all, the Pyre Guard could scarcely keep up.Only as the majority of the Salamanders crested the first ridge, did they first see the arc of fire. It trailed, long and blazing, into the darkling sky. The tongue of flame climbed and upon reaching the apex of its parabola bent back on itself into the shape of a horseshoe. Rockets screaming, it came down in the midst of the charging Salamanders and broke them apart. A savage crater was gored into the Urgall hills, like the bite of some gargantuan beast resurrected from old myth and birthed in nucleonic fire. It went deep, right into the beating heart of the Salamanders' ranks. Only by virtue of the fact that they were so far ahead were the Pyre Guard spared the worst. In a single devastating strike, the Lord of Iron had crippled the XVIIIth Legion, severed its head and sent its body into convulsive spasm. Retreat was the only viable strategy remaining. Droves fell back to the dropsite, trying to climb aboard ships that were surging desperately into the sky to outreach the terrible storm of betrayal below. It was not a rout, though for any force other than the Legiones Astartes it would have been, faced with such violence. Many were cut down as the traitors threaded the air with enough flak to wither an armada.Despite a heroic defence, the three Loyalist Legions who took part in the battle on Istvaan V were practically destroyed; all but a handful of Battle-Brothers fell on that fateful day and the Primarch Ferrus Manus of the Iron Hands was beheaded by his former best friend Fulgrim, the Primarch of the Emperor's Children. After this sad defeat, the Salamanders, as well as the other two betrayed Space Marine Legions, were unable to perform any further tasks the Emperor had planned for them and spent the rest of the Heresy rebuilding their shattered forces. Both Vulkan and his brother Corvus Corax survived the ambush on Istvaan V. Conflicting reports by the few survivors stated that Vulkan, also gravely wounded, had to be dragged away from the fight onto a Thunderhawk gunship by three of his surviving Pyre Guard and then managed to escape back to Nocturne. But the reality of the Salamanders' Primarch's fate would prove to be far more dire.