Isstvan III Atrocity - The Traitor's Dawn: Nearly two full solar months had passed on the dead hulk of Isstvan III when at last the great thunderstorms began to wan sufficiently for the Traitors to recommence significant landings of reinforcements and munitions once more. The months had seen the attacking forces bled for each city-block and kilometre of rubble they took and rough estimates put the death toll as high as 20,000 on the Loyalist side and perhaps twice as many of the attackers had been slain. Loyalist resistance still commanded the Precentor's Palace despite the best efforts of the Emperor's Children and the World Eaters to take it by storm, while Loken's Luna Wolves still dominated the sector that surrounded the Siren Hold as their killing ground.To the northwest, however, the Death Guard's implacable advance had caught the Loyalists between hammer and anvil, and steadily forced those that could not fight their way clear into an ever smaller pocket of resistance. And that noose was tightening. The only reversal for the Traitor Death Guard had been the rebellion of some of its heavy siege armour, whose crews bore loyalties to those their Primarch now called enemy and either refused to fire on their former comrades, or who in some cases turned their Siege Cannon on Mortarion's Traitors or Angron's World Eaters instead. It was notable in hindsight, and perhaps would be a telling factor on Isstvan III, that a proportionately high number of Death Guard Legion war machine crews were of Terran blood by the time of the Atrocity. The resulting blood fiasco devolved into a five-hour running battle, known by the Death Guard who survived it as the "Veil of Grief" during which the legendary resolution and discipline of the XIV Legion broke down for a time.Traitor and Loyalist became lost in a maelstrom of battle, firing on friend and foe alike. The Traitor Death Guard Marshal Durak Rask and his command squad were slain to a man by the Loyalist Crysos Morturg's Destroyer Squad, and the Death Guard Primarch himself is said to have suffered hurt, burned by plasma fire from a Predator tank in his own Legion's livery before he and his Deathshroud bodyguard hacked it to pieces. Only by issuing the order to withdraw and regroup did Mortarion bring the debacle to an end, although the respite had bought time for a force of Loyalist Death Guard to escape before Mortarion's grasp tightened again around the Loyalists.As the storms faded, fresh companies of Traitor Legionaries, tanks and heavy armour made planetfall on the outskirts of the Choral City in substantial numbers, and the Loyalist Death Guard enclave was the first to suffer as Mortarion poured his Legion's strength into the area. What Malcador heavy tanks salvaged from the Isstvanian defence armouries and turncoat armour the Loyalists had assembled proved no match for the forces ranged against them and were soon swept aside by Fellblade squadrons and long-range fire from the Titans ofLegio Mortis. Now in complete command of the field and surrounding the Loyalists' last redoubts, the Traitor Death Guard came on in wave attacks, their Tactical Squads so densely packed they advanced shoulder to shoulder across the torn-up ground, Bolters blazing in unison. The Loyalists did not give up, however, despite the insurmountable odds they faced, manning their few captured artillery pieces until they ran their munitions dry, and matching the storm of incoming fire as best they could until the barrels of their own Bolters glowed like hot embers and the barrel-shrouds of their Meltas cracked and buckled from over-use. It was all to no avail and the Death Guard Legion overcame the Loyalists' barricades and trench works like a black tide and drowned them. What few Loyalist survivors remained retreated to their last stand, deep into the lowest reaches of the sub-surface defence tunnels and collapsed the passageways behind them. But the Traitors had prepared for such eventualities, clearing the way with Vortex charges and Hades drills. Mortarion himself came for his former brethren in the darkness.Above ground, the assault was renewed in earnest, and the Warmaster unleashed his wrath. A Sons of Horus taskforce 30 companies strong and led by First Captain Ezykyle Abaddon and his elite Justaerin Terminators landed to the city's southwest with heavy armour support. They immediately set about crashing through the burned and blackened tenements they found there in ever widening circles, flushing out and destroying any pockets of Loyalist resistance they encountered. With the attack now fully underway once more, great orbital conveyors began to land fresh maniples of Titans from the Legio Mortis and the Legio Audax to reinforce those that had sat out the great firestorm and the terrible hurricanes untouched beyond the city, darkening the skies of the west. In the shadows of these colossal landers, a rag-tag assortment of stranger craft followed: black insectile gunships descending on columns of azure flame and battered civilian lighters with hulls bedecked with human body parts and daubed with strange symbols shuddered on the ground. From the first came black-robed Hereteks of the Dark Mechanicus bearing macabre weapons, robotic spider-skulls scuttling before them and multi-headed battle-automata, each large enough to dwarf a Legiones Astartes Dreadnought, grinding after them in their wake. But as outlandish and sinister as these Dark Mechanicus war machines undoubtedly were, the wasted, scarecrow figures that issued from the charnel bedecked lighters carried with them such a palpable aura of horror and sickening power that even the hardened Space Marines drew back warily where they walked. They were the Witch-Priests of Davin's Serpent Lodge and the taint of the Warp hung heavily around them like an unseen, worm-ridden shroud.The tide was quickly turning and while the Loyalists had held out thus far, the advantage was now the Traitors' to lose. They had their former brethren outnumbered and vastly outgunned, and were able to leverage their superiority of arms at last, while every dead Loyalist Astartes was now a loss the defenders could not afford. The mathematics of slaughter had now swung decisively in Horus' favour.