The famed "Promised Land" was a fabled subterranean metropolis nestled far below Taris's surface. Specifically, it lay beneath the Undercity and its intricate sewers, as well as the Lower City, Middle City, and Upper City. This location marked the original settlement site for the first Tarisians, a millennium before the planet's transformation into a major trade center and while the world was still covered by forests and oceans. The Taris Civil Authority held governance over it. This was prior to the Tarisian Civil War, which transformed the planet's non-urban areas into desolate wastelands. Entrance into the colony was a one-way journey, ensuring the secrecy of the Promised Land. According to Gendar, the journey to its entrance would span weeks or even months, requiring passage through numerous rakghoul-infested zones.
During the Manderon Period, a group of human ships of unknown origin established a colony on the planet. They began constructing an underground city that, according to Rukil, would become the Promised Land. By 5300 BBY, the city was complete, and the Taris Civil Authority governed the realm. As the population expanded, Transport Station 5 was erected atop and around the original colony. Another city was built above it, evolving into the Undercity, which included the sewers. Subsequently, the Lower City, Middle City, and finally the Upper City were constructed, leading to the abandonment and forgetting of the Promised Land. After more than a century of prosperity, new, shorter trade routes emerged, rendering Taris obsolete. By this time, the Promised Land had been rediscovered. A century later, following the Tarisian Civil War, criminals were exiled to the Undercity. These outcasts established a village but faced starvation, rakghoul attacks, and infections. Their only hope rested on the legendary Promised Land, which had since been lost.
The Outcasts passed down tales of the Promised Land through generations. These stories remained relatively popular during the Jedi Civil War, although belief in such a place was scarce. Nevertheless, Rukil, the Outcasts' elder in 3956 BBY, believed he could locate the Promised Land by piecing together his deceased father's and grandfather's journals. He also dispatched his apprentice, Malya, to find it, but she never returned. Rukil's efforts were opposed by the shady shopkeeper Igear, who feared that the Promised Land's discovery would diminish his status and the importance he gained from his salvage shop, the Outcasts' primary source of income.
During his forced stay on Taris in 3956 BBY, Revan visited the Undercity while searching for the Galactic Republic escape pod used by Jedi Bastila Shan to flee the Republic capital ship Endar Spire. He located the three journals—those of Rukil's apprentice, father, and grandfather—and presented them to Rukil. This information sufficed for Rukil to pinpoint the Promised Land's location. The following night, the Outcasts departed the Undercity, heading for the lost colony.
Regrettably for the Outcasts, Darth Malak soon ordered a devastating orbital bombardment of Taris. A group of heroes discovered during the Cold War that the Outcasts had indeed found the Promised Land; however, it differed significantly from the legends, especially after the destruction of Taris.
The buildings, equipment, generators, and possibly the droids had been destroyed, forcing the Outcasts to rebuild from scratch. Despite the challenge, they survived the bombardment. Many generations passed, each with a "Promised One" responsible for preserving the memories of the terrible apocalypse and leading the colonists.
The anti-Rakghoul serum that Revan discovered protected the initial generations, but the Rakghouls evolved resistance to the antidote, and babies could not be born immune. Some Rakghouls even evolved into sentient Nekghouls (who, unlike Rakghouls, could not spread the infection). The Outcasts eventually abandoned the Promised Land and recolonized the Undercity, renaming themselves the Tarisians. This proved futile, as the Tarisians continued to perish on the surface from starvation, disease, and Rakghouls, eventually becoming sterile. The last successfully preserved time recording revealed that the final generation had lost so much knowledge about the world that they were unaware of their origins or purpose. The remaining members ultimately succumbed to toxic waste, leading to the group's extinction. Information about them was lost until Republic forces recovered their post-apocalyptic history from both the Promised Land and the Undercity, sharing it with a local Republic historian. The Promised Land, like the rest of Taris during the Cold War, was later conquered and occupied for an unknown duration by the Resurrected Sith Empire.