The Jedi Order established a chapter house on the planet Aleen in the distant past. The chapter house was the site of the Great Seal, the artifact which separated the surface world and the Underworld; historians debated which preceded the other. For unknown reasons, the Order abandoned Aleen and their chapter house, allowing it to fall into disrepair and eventually collapse.
During the Clone Wars, circa 21 BBY, the Galactic Republic established an excavation site at the ruins of the chapter house where Republic researchers attempted to understand the groundquakes plaguing the world. During the mission, C-3PO and R2-D2 were led to the site by Aleena guides and they both accidentally fell into the hole. After working with the Kindalo and the mysterious being called Orphne, R2-D2 closed the Seal, restoring the balance on Aleen.
- Star Wars: The Clone Wars – "Mercy Mission" (First appearance)
- Star Wars: The Clone Wars – "Nomad Droids" (Appears in flashback(s))
- Nexus of Power (First identified as Jedi chapter house)