Coronid Deeps - Horus Heresy: During the Horus Heresy, the Coronid Deeps was effectively cut away from regular direct contact with the Segmentum Solar owing to the rising tide of Warp turbulence which would culminate in the so-called "Ruinstorm", which followed on from the dark events at Calth in 007.M31. What came to be known as the Manachean War was a campaign carried out by those under the direct command of the Warmaster Horus during the latter part of 007.M31.It was both an early example of the Warmaster turning his forces to seize entire sectors of the Imperium he deemed valuable to his cause, and a demonstration of the speed and brutality with which such campaigns were accomplished. It can be seen in retrospect to have provided a template for scores of such campaigns which came after it, both in terms of strategy and the savage consequences involved for those worlds which fell into the Traitors' grasp throughout the time of the Horus Heresy's Age of Darkness. The Conquest of Manachea, led personally by Horus and his inner cadre of commanders, was itself the centrepiece of an interlinked series of campaigns, fleet actions and local wars which swept like storms through the celestial region of the Coronid Deeps.Manachea itself was the jewel of the region; a highly-populated, highly-advanced Hive World of the first rank which sat at the centre of its own well-developed sub-domain of attendant star systems called the Manachean Commonwealth. As such, it offered the Warmaster much that would be of value in the ongoing galactic civil war, not least of all strategic control of the region, and vast Human resources to exploit as well as industrial capacity that could be readily turned towards the war effort.Nearby sectors also included the mineral-rich Cyclops Cluster -- home to two fully-fledged Mechanicum Forge Worlds, the vital Armada Imperialis fleet anchorage of Port Maw, several independent Knight Worlds, and a score of Agri-worlds and other colonies that could be used to feed and supply Horus' armies on the long march to Terra. These prizes were not, however, unguarded. Although the Traitors' agents had already been at work in the region, the bulk of its worlds and military strength was already set against him, the region's Imperial Commanders alerted by the wildfire warning that had spread after the news of the Isstvan III Atrocity had reached Terra.That such a warning had been issued in the region (whereas many other sectors and domains had been kept ignorant at first of the betrayal) was a result of the frontier's own proximity, in relative terms, to the Isstvan System itself; Port Maw being used as a layover and resupply base for a number of the fleets despatched so disastrously to punish the Traitors at Isstvan V.With only a few notable exceptions, the garrisoning of the Imperial worlds of the Coronid Deeps was provided for by the Imperialis Armada and regiments of Solar Auxilia Pattern Excertus Imperial Army formations. The Solar Auxilia Pattern was particularly suited to the defence of the region as it was equipped and formed to fight in hostile environments and participate in void battles, both of which were common in this far-flung domain of the Imperium, while the high technological base of worlds such as Manachea and Agathon made the requirements of Solar Auxilia Pattern regiments possible to maintain in a manner that was simply untenable on the majority of Imperial colony worlds.These defenders had shown themselves repeatedly able to withstand the assaults of xenos raiders, rebel uprisings and, on occasion, wholesale invasion -- at least until reinforcements arrived. They were well provided with arms, and warships, and numbered in the hundreds of thousands in terms of active troops. They had never though been measured against the unthinkable opponent, the Imperium's own Space Marine Legions.So it was that in the closing days of 006.M31, terrifying reports, quickly suppressed, reached the governing courts and councils of the Coronid Deeps that the unthinkable had occurred; that the Traitors had crushed those sent to bring them to heel at Isstvan V in the so-called "Drop Site Massacre." These reports were at first scoffed at and wilfully disbelieved, until the first few battered voidships, Loyalist survivors of the void battle at Isstvan, began to limp in, seeking sanctuary from the hounds of Horus at their heels.Fear came then to Manachea, to Agathon, to Mezoa and a hundred other worlds greater and lesser along the frontier. Requests for aid and instruction from Terra were lost on blinding squalls of Warp static, and with the Warp storms behind them and the black void of the frontier before them, the worlds of the Coronid Deeps could do little but wait for the devil to come for them from the dark.By the dawn of 008.M31, the Coronid Deeps, once a stable outpost of the Imperium, had become in part a fractured series of Traitor-ruled domains in a wider galaxy riven with strife. But this too was soon to be challenged as the spirit of war that had been unleashed would not be so easily assuaged, and for some victory was to prove fleeting. The counter-invasion of Numinal and the catastrophic destruction visited on Gethsamaine would only be the start of a new phase in the ongoing war for the Coronid Deeps. What would follow throughout the Coronid Deeps would become a protracted and bloody series of campaigns and battles with no certain victor.Outposts were raided, planets laid to waste, convoys ambushed and murderous reprisals taken; the tables frequently turning so that the hunters became the hunted and back again, and where one side gained an advantage, it was quickly squandered or laid low by sudden reversal of fortune. Loyalist and Traitor clashed again and again; forces came and went from the region as the tides of the unquiet Warp allowed and battle waxed high and waned in bloody exhaustion, only to be taken up again.So it was with the Coronid Deeps; so it was to be all across what was once the unified Imperium of Man. A grim age of war had been born at Isstvan III that would never end in the lifetimes of those who were caught in its bloody embrace, an age of war that would outlast the Horus Heresy, outlast the Great Scouring and beyond, an Age of Darkness never to truly end in the ten millennia to come.