In the Outer Rim Territories, far from any significant hyperspace lanes within the galaxy, specifically in the Subterrel sector, existed Polis Massa. It was located within a dense asteroid field and was classified as a planetoid. Once, Polis Massa was a full-fledged planet nestled in the system bearing the same designation. The Eellayin, a subterranean civilization, inhabited this planet until ancient superweapons brought about its destruction. Despite the catastrophe, the rocky remnants of the planet held Eelayin artifacts, which were subsequently gathered and analyzed by Kallidahin archaeologists.
To investigate the reasons behind the planet's destruction, the Archaeological Research Council of Kallidah established a base on one of the largest asteroids in 519 BBY to conduct excavations throughout the asteroid belt. Few traces of the Eellayin, their forebears, remained. However, in 69 BBY, researchers discovered the remains of the underground city known as Wiyentaah. Following this discovery, the Local Dig project was initiated and gradually expanded. The Kallidahin eventually became known as Polis Massans, a name derived from their extensive time spent on the planetoid.
After the implementation of Order 66, Polis Massa provided sanctuary for surviving Jedi. Shortly following the lightsaber duel between Obi-Wan Kenobi and Darth Vader on Mustafar, Senator Padmé Amidala delivered twins, Luke and Leia, at the medical center located on Polis Massa. Simultaneously, Yoda made contact with the deceased Jedi Master Qui-Gon Jinn, who informed Yoda that he would instruct him in the art of retaining consciousness after death. After giving birth, Leia was entrusted to Senator Bail Organa, while Luke was ordered to be placed under Obi-Wan's protection with the Lars family. Yoda, with Qui-Gon's presence, spoke to Obi-Wan, informing him that he too would receive training from Jinn on how to preserve his consciousness beyond death.
During the Galactic Civil War, Polis Massa functioned as a regional headquarters and operational sector for the Alliance to Restore the Republic. Polis Massa was marked on a galaxy map, identifying it as one of the safe worlds, a starfighter hub at level five or higher, a regional headquarters and operations sector, and a deep space cache location.
Vader's visit was motivated by his desire for retribution against those who had concealed his son from him. Subsequent to capturing Amidala's tomb on Naboo, Vader journeyed to Polis Massa accompanied by his death troopers and forensics droid ZED-6-7, seeking answers. Upon arriving at the ruins of the Polis Massa Base, ZED-6-7 revealed that Polis Massa had previously served as a rebel base before being bombarded by the Empire years prior. The Amidalans, believing Vader responsible for the deaths of Amidala and Skywalker, pursued him there, seeking to kill him. Vader deflected the attacks from their ships, and his death troopers seized control of the cannons, destroying numerous enemy ships. The Amidalans attempted a ground assault, but were swiftly defeated by Vader and his death troopers. When ZED-6-7 discovered a damaged Chroon-Tan B-Machine midwifery droid, he accessed its memory and retrieved footage from the day Amidala was brought there. Vader then viewed the recording of Amidala's final words, in which she expressed her belief that there was still good within Anakin. Enraged by this, Vader destroyed the droid and returned to Coruscant.
Polis Massa, which was initially referred to as Polis Matza during the scripting phase of Revenge of the Sith, was created for the 2005 film Star Wars: Episode III Revenge of the Sith. Slowed-down footage of the asteroid field from Star Wars: Episode V The Empire Strikes Back was used as a temporary placeholder for Polis Massa in the evolving edit of Episode III. In the DVD commentary for Revenge of the Sith, John Knoll mentioned that George Lucas intentionally designed Polis Massa to pay tribute to the appearance of the Clavius moon base featured in the 1968 film 2001: A Space Odyssey.