Consolidator

The Consolidator was a huge spaceship. The Time Lords imprisoned the Sild on it, along with a large amount of dangerous technology. The ship travelled for billions of years until it finally drifted into orbit around Praxilion. The inhabitants raided the Consolidator for its technology. After six thousand years, they reached the area where the Sild were confined and unintentionally released them.

The Sild fought the Praxilions for half a million years. Then they picked up a distress signal that was sending to a future self to free him from incarceration by UNIT. They captured hundreds of incarnations of the Master, rendered them unconscious, then brought them to the Consolidator and used them to create time ruptures to obtain the Master who sent the original signal.

The Third Doctor freed the Master from his prison on Earth before the Sild could capture him. They travelled to Praxilion in the far future and destroyed the Consolidator, and all the Sild onboard. (PROSE: Harvest of Time)