- "Welcome to the Spire on Stygeon Prime, the only Imperial detainment facility in the Stygeon system—and it's impregnable."
- ―Sabine Wren
The Spire, also known as the Stygeon Prison, was a secret, remote prison fortress located on the planet Stygeon Prime. The prison was operated by the Confederacy of Independent Systems during the Clone Wars. The Sith Lords Darth Sidious and Count Dooku held Darth Maul in the prison before he escaped with the help of Death Watch.
Years later, the prison was operated by the Galactic Empire. The Empire protected the prison with ray shields, blast-proof structures, anti-aircraft weapons, TIE fighters, and stormtroopers. The rebellious crew of the Ghost learned that the Empire was holding Jedi Master Luminara Unduli in the prison and attempted to save her. During the attempt, former Padawan Kanan Jarrus encountered the Grand Inquisitor.
During the Clone Wars, the Confederacy of Independent Systems secretly operated the Spire. Following Darth Sidious' capture of Darth Maul on Mandalore, Maul was taken by Sidious and his apprentice Count Dooku to the Separatist's secret prison on Stygeon Prime. There, Maul was brutally interrogated by Sidious and Dooku. After Sidious left, Dooku continued interrogating Maul for information on his Shadow Collective and his underworld contacts. However, a pair of Mandalorian super commandos, Commander Saxon and Rook Kast, were sent by Mandalore's Prime Minister Almec to free Maul. They were able to liberate Maul, escape the prison and evade the prison's battle droid garrison.
Following the end of the Clone Wars, the Spire came under the control of the newly formed Galactic Empire. After her capture, Jedi Master Luminara Unduli was imprisoned there and later executed. Her remains were kept in her former cell in order to lure out any survivors of Order 66. Five years before the Battle of Yavin, Imperial senator Gall Trayvis, posing as a dissident, leaked information on the Spire, claiming that Master Unduli was alive. The news was received by the Lothal rebel cell, who acted on the information, hoping to free her. Cell leader and Jedi Kanan Jarrus and his team were able to infiltrate the Spire, however Jarrus and his apprentice, Ezra Bridger, discovered that Unduli was in fact dead. The Grand Inquisitor revealed that Unduli had died with the Old Republic and that her bones were meant to lure the last of the Jedi out of hiding. Jarrus dueled the Inquisitor, but was outmatched. He and the other rebels were able to make their escape past the Spire's stormtrooper garrison and escape.
- Darth Maul—Son of Dathomir, Part One (First appearance)
- Darth Maul—Son of Dathomir, Part Two (Indirect mention only)
- Droids in Distress book
- Star Wars Rebels – "Rise of the Old Masters"
- The Inquisitor's Trap
- Sabine My Rebel Sketchbook
- Star Wars Rebels: The Visual Guide (First identified as Spire)
- Ultimate Sticker Collection: Star Wars Rebels
- Ultimate Star Wars
- The Official Star Wars Fact File 72 (STY1, Stygeon Prime - The Spire)
- Star Wars: Absolutely Everything You Need to Know
- Star Wars Character Encyclopedia: Updated and Expanded
- Star Wars: Galactic Atlas
- Dawn of Rebellion
- Star Wars Encyclopedia of Starfighters and Other Vehicles (Indirect mention only)
- ; image #2 (of 8)
- Star Wars: The Card Game – Galactic Ambitions (Card: Encounter at Stygeon Prime)