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Battle of Thoas

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Battle of Thoas
Lord of Ultramar.png
Guilliman leads the Ultramarines on Thoas
Conflict Great Crusade
Date After 903.M30
Location Thoas
Outcome Imperial victory
Ultramarines Orks
Primarch Roboute Guilliman
Chapter Master Primus Marius Gage
6th Chapter Master Atreus
9th Chapter Master Klord Empion
11th Chapter Master Vared
16th Chapter Master Evido Banzor
22nd Chapter Master Eleon Iasus
Ork Emperor of Thoas
12 Chapters:
Invictarus Suzerains
1st Chapter
6th Chapter
9th Chapter
11th Chapter
16th Chapter
22nd Chapter
Millions of Orks
Severe Total

The Battle of Thoas was a battle fought during the Great Crusade between the Ultramarines and orks on the world of Thoas shortly after the razing of Monarchia. It was the last battle in the systematic extermination of an Ork empire that once spanned a dozen systems.[1a]


On the surface of Thoas, the Ultramarines identified the remains of a pre-Imperial human civilisation. The ruins were as large as the mountains amongst which they were built, and infested with the highest concentration of orks the Ultramarines had encountered in the campaign. Captain Hierax recommended the use of the Nemesis Chapter's Destroyers to purge the orks, but this was rejected by Lord Guilliman in favour preserving the history of the extinct human civilisation.[1a]

The Ultramarines deployed their forces on the plains beyond the fortress, drawing the orks out of the ruins with the promise of open battle in order to bombard the approaching horde with artillery. Guilliman personally led the spearhead of the First Chapter into the resultant confusion,[1b] with the other eleven Chapters following behind. The orks' front line was ten miles wide, engulfing the Ultramarines until they were surrounded. The Ultramarines fought through the horde to the ruins, fortifying a series of pyramids that had once served as military redoubts. Guilliman determined that the human civilisation was pre-Gothic, and its fall into ruin pre-dated the occupation by the orks. Techmarine Loxias of the 221st Company estimated a battle fought with bio-alchem weapons fought at least a thousand years earlier based on radiation levels, whilst Guilliman had reckoned the orks' presence to have been as recent as a century or two.[1c]

At the northern end of the line of pyramids, the 22nd "Nemesis" Chapter came under heavy attack from orks emerging from the network of underground tunnels beneath the fortress-complex. The other pyramids soon came under attack by the same means, as well as the orks launching simultaneous assaults on the fortress walls. In the tunnels beneath the northernmost pyramid, Captain Sirras of the 223rd disobeyed the orders of the newly appointed Chapter Master Iasus not to employ lascannon, resulting in a tunnel collapse that buried the Nemesis Chapter.[1d]

Guilliman ordered an airlift to carry forces of the First Chapter to the northern pyramid, which had collapsed in on itself along with the tunnels below. The survivors of the Nemesis Chapter, cut off from the surface, pressed deeper into the tunnels.[1e] Guilliman's intervention eased the pressure on the 16th Chapter, allowing them to link up with the 9th. The two Chapters broke out to the south, reinforcing 6th Chapter on the southern front. Based on the higher concentration of both orks and radiation in the northern sector, Captain Hierax reasoned that there was a cache of rad-weapons beneath the surface. Petitioning the primarch, Hierax was given permission to deploy the Second Destroyers, who had been left in orbit aboard the Cavascor, via Drop Pod.[1f]

Caught between the First Chapter and the Second Destroyers, the ork horde began to thin in the northern sector. The Ultramarines force then made their way to Chapter Master Iasus's surviving forces beneath the surface, where they had been embattled by orks coming from below. There, they discovered a switchback ramp going deep beneath the surface, designed for bringing entire convoys of ordnance transporters to the surface.[1g] At the bottom, they found a cavern three hundred metres high. Extreme radiation spike indicated that the weapons within, including shells for a Baneblade and missiles the size of a Deathstrike, were bio-alchem and phosphex rad-weapons.[1h]

The Ork Emperor of Thoas sat on a throne built from a huge number of missiles, rockets, and bombs collected in the centre of the chamber and welded together in an act of insanity or faith. Guilliman climbed the mound and engaged the emperor in combat, unwilling to use the Hand of Dominion in case its energy field set off the munitions. As the ork held the primarch aloft in triumph, Guilliman fired a sustained burst from Arbitrator into its maw, ripping it apart from the inside without striking the mound of ordnance.[1h]


In the aftermath of the battle, Guilliman came to the conclusion that the human civilisation that had built the fortress complex had been destroyed by a civil war using bio-alchem weapons. He gave the weapons remaining in the throne room to the Second Destroyers and ordered the fortress-complex to be flattened by orbital bombardment, believing that the history was unprofitable to future settlers, a memory that had no place in his Father's Imperium.[1i]

Many years later, during the Great Scouring, Guilliman led a protracted action against the Iron Warriors on Quradim. Despite the Imperial losses in the campaign, Guilliman decided against enacting exterminatus on Quradim, citing Thoas as an example of what he was hoping not to achieve.[2]

See also