Battle of Trisolian

The Battle of Trisolian
Date	~011.M31
Scale	Void battle
Theatre	Horus Heresy
Status	Imperial retreat
Belligerents
Space Wolves	Sons of Horus
Commanders and Leaders
Leman Russ, Belisarius Cawl	Horus
Strength
~40,000 Marines, the near entirety of remaining Space Wolves; Mechanicum loyalists	~50 capital ships; Sons of Horus Legion; elements of Word Bearers, World Eaters, Alpha Legion, Night Lords & Iron Warriors; Mechanicum Traitors
Losses
Extremely High, several companies reduced to less than 20% strength	Not known
Outcome
Effectively ended the Space Wolves as a "Legion", who retreated to Yarant. Horus badly wounded/partly de-corrupted. Leman Russ badly wounded and/or traumatized.

The Battle of Trisolian is the ill-fated attempt by Leman Russ to kill Horus before the inevitable Siege of Terra. It also marks the earliest appearance of a young Belisarius Cawl who is a mere up-and-coming but still notoriously unconventional tech-adept by this stage.

Background

Late in the Horus Heresy, the Space Wolves legion had lost around 25% of their forces at Prospero and had taken a further maulings at the Battle of the Alaxxes Nebula, coupled with engagements at Vanaheim and Daverant, reduced their number to around forty thousand marines. Following Alaxxes the remnant returned to Terra to coordinate with the loyalist forces.

Leman Russ sponsored a stealth mission by the Knights-Errant on the Vengeful Spirit during the Battle of Molech in order to gauge any weaknesses in the traitor dispositions and report back on the state of Horus himself. However, the mission went sour when they were discovered, leading to the deaths of several of the Knights-Errant involved when the Warmaster decided to make examples of them.

Following the completion of this mission, Sanguinius and Jaghatai Khan had also arrived on Terra and convened a war council to determine the next course of action: Rogal Dorn urged that all remaining forces maintain a defensive posture, but was appreciative that the Ultramarines and Dark Angels were assaulting the traitors' rear and providing relief to loyalist forces, allowing them to dictate the next few battles. Dorn declared that Terra was too confined a battlezone for the loyalist contingent of Titan Legions and so proposed a muster at Beta-Garmon and make a stand there in order to give time for Roboute Guilliman and Lion El'Jonson to crush the traitors in a pincer movement. The Battle of Beta-Garmon would itself become the site of one of the greatest battles in the entire Horus Heresy.

However, Leman Russ would not be swayed from his original plan and chose to depart from Terra for Fenris in order to scry a weakness in the superhuman upgrades that Horus gained at Molech, determining that he should take the oft-maligned "Spear of Russ" with him.

The Battle

The battle itself took place over the Forge World of Trisolian A-4, which had recently been captured by traitor forces following a surrender of Mechanicum forces, although a loyalist faction of Skitarii led by Cawl continued to fight against the traitors.

Russ really wanted Horus's wolf pelt

The Space Wolf fleet used the unique gravitational properties of the three stars of the Trisolian star system to approach with stealth and speed, using most of their ships as a distraction while Russ own flagship engaged the Vengeful Spirit directly, allowing him to board with thousands of marines.

Russ had already figured that the battle would result in a loss for his forces, but thankfully Cawl's loyalist Mechanicum elements on the Forge World managed to overthrow the regime and revert the planet back to loyalist control, allowing it to lend a hand in the conflict.

Once aboard the flagship, Russ engaged Horus directly in an extremely savage duel and incredibly, managed to best Horus, scoring a debilitating wound with his spear and literally (not figuratively) bringing Horus to his knees. Russ' Spear had been made by The Emperor himself, and so contained some of his power, and as everyone here knows, that power is anathema to Chaos, so when Chaos-juicing Horus was wounded by it, the effect was even more destructive than it might otherwise have been. In point of fact, this power was so pronounced that when Russ began to further run him through, Horus was shown to visibly terrified, not by Russ, the wound, or even the very real prospect of death at the hands of his brother, but of the spear's ethereal power coursing through him, obliterating the effects of his chaos-juicing, and wrecking his massive gains. Unfortunately, Russ was then beset by a rampaging plot device by way of narrative cliché that momentarily overcame his better judgment and stated goal. Thus, instead of immediately killing Horus like he should have done (that was precisely the primary mission objective remember) the wound gave Horus a brief moment of clarity, and so despite the sacrifices made of himself, his sons, and some of his closest advisors (like the death of his chief Rune Priest, Kva), not to mention having heavily negatively impacted Dorn's defensive plans for the upcoming siege by leaving Terra, now, with the Arch Traitor himself at his mercy, Russ instead tried to plead to his brother to rejoin the Emperor's fold. Horus rejected and then suckerpunched Russ, starting a new duel. Horus was about to kill him, but was prevented from delivering the killing blow by a mob of dozens of Space Wolves who literally dogpiled him, allowing Bjorn to drag Russ from the battlefield and back to the Loyalist fleet where they began to disengage and retreat.

Aftermath

Already heavily depleted from all the military actions since Prospero, following Trisolian, the Space Wolves were mauled further still, with some companies being reduced to less than a fifth of their already diminished forces, leaving their effective fighting force to, at best, somewhere in the range of 10 to 15 thousand marines. While that number may still sound a tad higher than expected, consider that A, this is all that they had to get through the rest of the war and the subsequent Scouring, B, they would eventually form an ill-fated Second Founding chapter, and C, the Space Wolves (like the Black Templars) at best pay only nominal lip service to the Codex Astartes and even in the 42nd millennium maintain a fighting force somewhere between 3 to 6 thousand marines. In any case, without any means of quickly replenishing their forces, this effectively ended the existence of the VIth Legion as a legion.

Horus, sour over the considerable losses his own forces had incurred and rattled that Russ legitimately could have killed him (even acknowledging it to himself) ordered a Certain Armless Failure to lead a contingent of his forces to hunt down the remnants of the 6th and not return without Russ' head. Disappointmaddon then returned without Russ' head. Oh, and without most of the marines Horus had given him as well.

With their Primarch unconscious from his injuries, the remaining Space Wolf commanders have to make a decision of whether to stay together and likely die, or disperse and play no further part in the Horus Heresy. Choosing to remain together to present a viable threat that the traitors would have to divert resources to deal with, they retreat to Yarant III to make a stand where they are hunted by Failbaddon but are eventually saved by Corax following his own gene-seed debacle.

Horus was partially cleansed of the corruption he gained at Molech after being wounded by the Spear of Russ and a momentary glimpse of the original Primarch is witnessed by his brother, granting him enough self control to reject the Chaos Gods but continued the campaign on his own terms. Lorgar believed that Horus' failure to submit to the gods' will but still accepting their gifts would lead them to withdraw their power when he needed it most and cause the war to be lost. Horus later fell into a coma at the aforementioned battle at Beta-Garmon as his wound reopened, and Lorgar attempted a coup.

A shard of Horus' soul that had been purified by the Spear of Russ would be fought over by the Chaos Gods, requiring the sacrifice of Maloghurst in order to free him and Lorgar was expelled from the Warmaster's fleet after his coup failed, with Horus warning that he would kill Lorgar if he ever saw him again.