Attack on Korriban During the fifth year of the renewed warfare between the Galactic Republic and the Sith Empire , the Eternal Empire made an attack on the planet Korriban . It was part of a series of preliminary raids by the Empire , which up to that point had been concealed to the rest of the galaxy , as a test of the strength of the border worlds of the Republic and the Sith . Korriban was a prime target for the Eternal Empire , due to the presence of the Sith Academy for the training of Acolytes . The twin princes Arcann and Thexan led the assault , where they faced fierce resistance . Arcann was critically injured during the battle , suffering severe burns and the loss of an arm and an eye . However , the following day he was on his feet again and executed the Sith commander Darth Atroxa . Despite the efforts of the Sith , the Knights of Zakuul breached the Sith Academy during the fighting . The attack was a tremendous defeat for the Sith , while the Eternal Empire only suffered moderate casualties . Following the battle , the forces of the Eternal Empire withdrew , eventually heading back to their throne - world of Zakuul . Shortly afterwards , the Republic and the Sith Empire joined together to find the source of these unknown aggressors . Prelude . Located in the Esstran sector of the Outer Rim Territories , Korriban was the homeworld of the Sith species as well as the subsequent Sith Order , though the Great Hyperspace War against the Galactic Republic saw the ruin of the Sith Empire . Millennia later , Vitiate , Emperor of the reconstituted Sith Empire , grew weary of the restraints placed upon him by the Sith and his Empire . Freeing himself , he split his consciousness into a new body — Valkorion , and set to work forging a new empire from the swamps of the planet Zakuul ; the Eternal Empire . The new realm became immensely powerful , all the while remaining concealed from the rest of the galaxy in Wild Space . Centuries later , the Sith Empire returned to the known galaxy , initiating the Great Galactic War against the unsuspecting Republic . Early in the war , the Sith stormed Korriban , overwhelming the few Republic defenders . The abandoned Sith Academy , previously used three centuries earlier during the Jedi Civil War , once again saw use , turning out only the most powerful Acolytes . Although the Treaty of Coruscant was signed decades later between the two opposing sides , the resulting tension between the Empire and Republic eventually overflowed , spilling into yet another war . In 3637 BBY , the fifth year of the conflict , Valkorion ' s twin sons , Princes Arcann and Thexan , proposed a plan to test the capabilities of the Republic and Empire in combat . Valkorion agreed , granting Thexan control of the Eternal Fleet — an armada operated by sentient droids , though he ordered that Arcann remain on Zakuul . However , Arcann disobeyed his father ' s wishes and led the assault alongside his brother regardless . They fought on many worlds , before finally striking at Korriban . The attack . The forces of the Eternal Empire , composed of starfighters , shuttles and at least three battleships descended on Korriban , facing fierce resistance from the Sith ' s own naval forces . The latter was comprised of Mark VI " Supremacy " - class starfighters and " Fury " - class Imperial interceptors . Led by Arcann and Thexan , the Force - sensitive Knights of Zakuul and several droids advanced on the Sith Academy on foot . They clashed with the Sith under the command of Darth Atroxa in the Valley of the Dark Lords , whose forces were composed of Sith Warrior s as well as Acolytes and Overseers from the Academy . During the battle , Arcann was grievously wounded . As several Knights stood guard , the surgeons operated upon him . The prince was later taken away from the battle to an encampment , where he thrashed in pain for hours before finally succumbing to sleep . There , Arcann was further performed upon ; by the end of the ordeal , he had been fitted with a replacement cybernetic arm and eye — the latter as a part of a durasteel mask made to protect the prince ' s burnt face and to intimidate his foes . While Arcann was incapacitated , Thexan updated Valkorion on the status of the battle via holocom . The emperor did not express concern over his son ' s injuries , remarking that Arcann had " paid the price for defiance " in leaving Zakuul . The following day , Arcann was on his feet again and led a renewed assault during an intense sandstorm . Darth Atroxa , the Sith commander , met her end by the prince ' s lightsaber after he used his cybernetic arm to twist her wrist . This disarmed her , allowing Arcann to land the finishing blow . Darth Hexid was among those Sith who joined in the defense , carving her path through the invaders until she was knocked out by an explosion . Despite Sith resistance , the Eternal Empire stormed the Sith Academy , where Sith Acolyte Veeroa Denz decapitated her Overseer , using the confusion to escape Korriban and the Sith . Aftermath . The attack was a crushing defeat for the Sith . Not only had they suffered heavy casualties , but considerable damage had been done to a prominent academy for the training of prospective Sith . The Eternal Empire also sustained sizable losses during the battle , though not as extensive as those of the Sith . As a result of the attack , many Acolytes fled and settled down to live their lives without interference from the Sith or the Eternal Empire , such as Veeroa Denz on Nar Shaddaa , while Darth Hexid despised the weakness of the Sith who bowed down to the Eternal Empire and went to wage her own personal vendetta against Zakuul . When the raids were concluded , the forces of the Eternal Empire returned to Zakuul . A joint Republic - Sith taskforce led by Darth Marr was dispatched to locate the source of these unknown assailants . During the ensuing skirmish with the Eternal Fleet , forces of the Sith Empire identified the starships of the Fleet as belonging to the same faction that had earlier attacked Korriban . Behind the scenes . The attack on Korriban made its first appearance in the cinematic trailer " Sacrifice " , released on June 15 , 2015 . The trailer promoted the then - upcoming expansion for the massively multiplayer online roleplaying game " " , titled " " . The attack served to establish how Arcann sustained his injuries and received his cybernetic replacements , which led to his change of personality to a darker tone .