The Great Temple, alternatively named the Massassi outpost, Base One, or the Yavin 4 Rebel Base, existed as a temple situated on the moon of Yavin 4. It functioned as the primary headquarters for the Alliance to Restore the Republic during the early stages of the Galactic Civil War. In their conflict with the Galactic Empire, the Rebel Alliance repurposed the ancient-looking stone structure, which notably included a grand ceremonial chamber, a control room, and a spacious hangar designed for starfighters. Following the events of the Battle of Yavin, the Alliance evacuated the Great Temple, and within a period of three years, they established and populated a new base of operations located on the snow-covered planet of Hoth.
The construction of the Great Temple occurred over 5,000 years prior to the Battle of Yavin. It was undertaken by a group of Massassi, a slave race who were once governed by the Sith, under the direction of the Sith Lord known as Naga Sadow. Speculation suggests that the temple's location held either sacred significance or importance for early scientific endeavors.
At some stage, whether as part of the original design or through later additions, the Ordu Aspectu utilized the Great Temple as a repository for data. This included a map room that provided directions to the Citadel of Rur situated on Garn.
The Massassi eventually faced extinction millennia before 0 ABY, after the completion of their temples. More than five thousand years following its construction, the Great Temple was rediscovered by the Alliance to Restore the Republic. Having abandoned their former base on the planet Dantooine to avoid detection by the Galactic Empire, the Alliance had its engineers transform the expansive structure into their operational headquarters, designating it as Base One. From the Massassi Base, Jyn Erso, K-2SO, and Cassian Andor embarked on a journey to Eadu. Subsequently, the Alliance launched a contingent of X-wings and Y-wings from the base towards the planet. Later, when Rogue One found themselves trapped on Scarif, almost all of the Rebel forces stationed at Massassi Base were dispatched with the Alliance Fleet to attack the planet.
Following a successful attack on the Empire's Death Star originating from the Temple, the Alliance was compelled to evacuate Yavin 4 due to concerns about potential retaliation. At some point after their departure, the Empire seized control of the Great Temple.
The Great Temple was a towering, pyramid-shaped construction, characterized by a series of progressively smaller levels and a spacious chamber with a high ceiling at its apex. It was constructed using enormous stone blocks extracted from the Yavin 4's surface, with no clear indications of sophisticated technology employed in its creation. After the Alliance to Restore the Republic assumed control of the building, they modified the Great Temple to suit their operational requirements. This involved excavating new spaces and reinforcing the interior walls using sheets of joined metal, as well as fortifying the stone floors with ferrocrete. The Rebels also installed elevators that provided access from the subterranean level to the open hangar area.
With the modifications implemented by the Rebel Alliance, the base possessed sufficient capacity to accommodate a minimum of sixty fighters and two Gallofree Yards GR-75 medium transports. The base's barracks provided accommodation for thousands of soldiers. Despite this ample space, the number of bunks available was insufficient for every soldier, leading some to create hammocks from cargo nets.
Located deep beneath the moon's surface were survival bunkers, connected to the temple via turbolifts. The Alliance installed these bunkers as a "last refuge" in the event of an Imperial planetary bombardment.