The conflict known as the Great Scourge of Malachor, alternatively called the Battle of Malachor, involved clashes between the Jedi Order and the Sith Empire. This battle took place on the planet called Malachor. During the confrontation, the Jedi launched an assault on the Sith temple, a battle station that also functioned as a superweapon with the capability to extinguish all life. The aftermath of this battle, characterized by combatants turned to stone, was preserved for numerous years following the Great Scourge.
Around 3966 BBY, Darth Tanis engineered the superweapon atop the Sith temple. Long before the Cold War, the Jedi Knights engaged in combat against the forces led by a Sith witch and the Sith temple located on the planet of Malachor. As the battle raged, the temple was activated, resulting in death for all beings present on the planet. The sole remnants were the petrified bodies of the warriors, strewn across the battlefield. Other ancient superweapons, powered by dark side energies, also played a role in the conflict. The dreadful events of Malachor would shape Jedi legends for millennia afterward, with accounts of the battle being shared as cautionary tales or warnings for Jedi younglings.
While training Darth Maul, Darth Sidious transported Maul to the battle site to impart knowledge to him about the downfall of the Sith. Sidious commanded Maul to inhale the ashes of his Sith predecessors. While breathing the ashes, Maul began to experience visions depicting the deaths of countless Sith warriors at the hands of the Jedi.
In 3 BBY, the fossilized remains of the battlefield were encountered by Padawan Ezra Bridger, Jedi Knight Kanan Jarrus, and former Jedi Ahsoka Tano. Tano, drawing upon her Jedi teachings, remembered that a battle had occurred on Malachor. Bridger questioned whether the Jedi had emerged victorious, but Tano concluded from the battlefield's remains that there were no winners. Bridger discovered a green-bladed crossguard lightsaber, briefly activating it before it malfunctioned. After Jarrus was blinded by Maul, he located a Jedi Temple Guard mask, donning it during a brief dueling encounter with Maul on the Sith temple's exterior.
The Great Scourge of Malachor was initially mentioned in the 2015 reference publication Star Wars: The Force Awakens: The Visual Dictionary. It noted that the crossguard design of Kylo Ren's lightsaber was an ancient design, tracing back thousands of years to the Great Scourge of Malachor. Pablo Hidalgo, a creative executive at Lucasfilm Story Group and the book's author, included the reference to connect it to the battle that was ultimately referenced in "Twilight of the Apprentice," the final episode of the second season of the animated television show Star Wars Rebels.
While the precise details of the Great Scourge remain unrevealed, Star Wars Rebels executive producer Dave Filoni has shared his perspective on the battle. According to his vision, the battle transpired when Jedi Knights attacked the Sith temple under construction by a Sith Lord. This Sith Lord's voice became the Presence within the obelisk activated by the Sith holocron that Ezra discovers in "Twilight of the Apprentice." In this concept, the temple either fired or malfunctioned, resulting in the petrified destruction that persisted on the battlefield for millennia.