Polis Massa was once an arid, habitable, barren planetoid and originally the homeworld of the origin of the little-known Eellayin civilization, who dwelt in underground cities such as Wiyentaah. Polis Massa was later struck by a mysterious cataclysm. This natural disaster destroyed the planet and formed a field of asteroids which remained known as Polis Massa, especially the largest of them. The Eellayin civilization disappeared.
About 519 BBY, the Kallidahin from Kallidah, another world in Subterrel sector, abandoned their homeworld and under the leadership of the Archaeological Research Council of Kallidah settled Polis Massa Base. They sought to prove the Eellayin were the ancestors of the Kallidahin through cloning tissue samples recovered in their digs. The most important find was the lost city of Wiyentaah (not far from the Research Base), discovered 59 BBY, began an archaeological mining project on this planetoid, to uncover the mysteries of the cataclysm and the native species it destroyed. The Local Dig was established over Wiyentaah. Such was the length of this project, the Kallidahin became known as Polis Massans themselves.
Excavations on the largest Polis Massa asteroids uncovered many prize artifacts, mostly from deep within the planetoid. The Polis Massans analyzed these artifacts for organic tissue suitable for cloning. Though the aliens frequented the Subterrel Sector, they had little contact with the galaxy and as a whole, the Polis Massa outpost remained remote and hidden.
Polis Massa was technically a loyal part of the Galactic Republic and friendly to the Jedi. Far from any major hyperlane, the remote settlement served as an emergency sanctuary for the Jedi after Order 66, during the rise of the Empire and Palpatine's Great Jedi Purge. The colony also housed the medical facilities in which Padmé Amidala gave birth to the twins Luke and Leia, and subsequently died because she lost the will to live. It was here that Bail Organa chose to adopt Leia into his family. When Yoda arrived with Bail, he was visited by the specter of Qui-Gon Jinn who offered to tutor Obi-Wan Kenobi, as well as Yoda himself, in the art of surviving one's death with the consciousness still intact. Shortly after Padmé's funeral on Naboo, Yoda returned to Polis Massa to retrieve a Kallidahin escape pod, to make his exile to Dagobah.
Not long after the formation of the Galactic Empire, the Inquisitors Malorum and Sancor began investigations of Polis Massa, discovering much information to be sent to Lord Vader. In a fateful run-in with Obi-Wan Kenobi at the Research Base, Sancor lost his life.
Galactic Civil WarEdit
During the first days of the Alliance to Restore the Republic, a movement that started in 2 BBY, the Rebel command mounted a secret base on Polis Massa. The base was crewed by beings of different species, including Human troopers, Wookiee archers, and Bothan spies. They were equipped with FX-series medical assistant droids and AAC-1 speeder tanks. The Alliance launched many operations from their Polis Massan base, although the Rebel Alliance did their best not to disturb the nearby Kallidahin excavations. The Empire raided this base repeatedly but the base survived these attacks.
In 0 BBY, the Polis Massan Rebel base received an important transmission from other Rebels: the plans of the Empire's new armored battle station. Knowing that the transmission had been made, Darth Vader ordered his agents of the 501st Legion to recover the plans and destroy the Rebel outpost. The Bothan spies, knowing that the Empire would have tracked the transmission, secretly forwarded the plans to another Rebel outpost, the Tantive IV starship, and prepared a forgery to trick the Imperial forces as much as they could. The Empire discovered the deception during the attack but was slow in issuing new orders to the 501st. Eventually, the 501st obliterated the Rebel presence on Polis Massa and found a new trail to follow, tracking Princess Leia Organa's corvette orbiting over Tatooine.
Yuuzhan Vong WarEdit
Polis Massa did not attract the attention of the Yuuzhan Vong and remained unscathed during the Yuuzhan Vong War.
Behind the scenesEdit
In the DVD commentary for Revenge of the Sith, John Knoll explains that George Lucas specifically designed the look of Polis Massa to be an homage to the look of the Clavius moon base in the 1968 film 2001: A Space Odyssey.