The Valley of the Jedi or the Valley of the Souls was the site of the Seventh Battle of Ruusan, the last battle of the New Sith Wars and a thousand years before the Battle of Yavin.
There, Lord Kaan's thought bomb trapped the souls of over one-hundred Jedi and Sith until they were finally freed by Kyle Katarn.
The Valley of the Jedi then became a concentrated area of Force energy called a Force nexus, and is widely believed to be the most powerful Force nexus in the entire galaxy.
At the close of the New Sith Wars, the Brotherhood of Darkness's situation had become so fragile that their leader, Lord Kaan, resorted to the use of a thought bomb to end the war.
Luring the Jedi deep into one of Ruusan's caves, Kaan and his Brotherhood detonated the thought bomb, hoping to wipe out Jedi Lord Hoth's Army of Light. However, Hoth perceived Kaan's strategy and left most of his army behind, taking only ninety-nine Jedi with him (one-hundred in total, including Hoth himself). This sacrifice was not in vain, as the Sith proved unable to control the thought bomb, killing the entire Brotherhood of Darkness and ending the New Sith Wars.
Jedi Knight Johun Othone, Hoth's former Padawan, went against the will of the Jedi Council to build a monument to the heroes of the Army of Light and Lord Hoth, with a mausoleum adorned with massive statues. He also placed a huge Adegan crystal in a meditative chamber for the Jedi. The monuments were made by stones that came from various planets, like the heroes of the Army of Light. The graves of the heroes were contained in a central underground cavern of natural origin, with several satellite chambers hewn around it. They were filled with artifacts that presumably belonged to the fallen Jedi warriors. At least one aqueduct brought water into the Valley.
It is believed that the spirits of the Jedi were trapped and the Bouncers of Ruusan said that they would be freed when a 'Knight' returned to release them.
Shifting nebulae soon erased hyperspace routes to Ruusan, leaving it inaccessible from the Galaxy at large. Because of the monument's "illegality," the Jedi Council forgot about the Valley which eventually became legendary. Yoda and a few others, including Luke Skywalker who learned about it from Yoda, knew about the Valley, but did not know its location or even whether it existed at all.
Over a millennium later, the location of the Valley had been lost to all but a few. The Jedi Master Qu Rahn believed that the Empire or the Dark Jedi would try to take advantage of the power trapped in the Valley and tried to keep its existence safe when his friend Morgan Katarn accidentally discovered its location.
Years after Jerec murdered Katarn, he and his minions learned of the existence of the Valley and captured Rahn, whom they executed after ripping from his mind the fact that Katarn had a map to Ruusan carved into the ceiling in his house. Traveling to Sulon, they took the map and began occupying Ruusan. There, Jerec basked in the power of the Valley, becoming almost godlike in his power.
However, his dominion of the Valley would not go uncontested. Rahn's spirit spoke to Kyle Katarn, Morgan's son, and instructed him in the Force. Katarn tracked down the map, only to have it destroyed before he could read it. He proceeded to hunt down 8t88, the droid that had deciphered the map, and retrieved the coordinates from his internal memory.
With the coordinates, Katarn and his partner Jan Ors made their way to Ruusan. After Jan was captured by Jerec's forces, Katarn fought his way through hordes of stormtroopers and defeated Jerec's remaining Dark Jedi minions until he finally confronted Jerec himself at the Valley's focus. There, he was able to cut off Jerec from the Valley's power and defeat him. Katarn freed the trapped spirits, finally fulfilling the Poem of Ages.
Right after Jan's "death" at the hands of Desann and Tavion Axmis, Katarn once again traveled to the Valley in order to make use of its residual Force energy to re-establish his lapsed connection with the Force. Unknown to him, he was tracked to Ruusan as part of Desann's plan. Desann moved in his forces and began using the Valley's power to boost that of mildly Force-sensitive recruits, creating the Reborn.
Fortunately, Katarn had revealed the location of the Valley to Luke Skywalker as a precautionary measure. Skywalker led Rogue Squadron to Ruusan and routed Desann's forces, driving him from the planet and cutting