Established on the moon Yavin 4 after the Rebels evacuated their base on Dantooine, the secret headquarters of the Alliance occupies several ancient Massassi ruins. The primary location is the round Great Temple, where the Alliance has an enormous War Room on the ground level, along with a Communications Center and many common rooms built into the ancient chambers.
The top of the temple houses an observation deck, and below that is the grand audience chamber. Under the chamber are housing levels for Alliance troops. Under the command of General Jan Dodonna, Alliance engineers cleared out the ancient structures and made them fit for habitation once more, and also erected high lookout towers. The structure's lower levels provide a secure hiding place for the Alliance's precious fleet of X-wing and Y-wing fighters.