The Silent Citadel

Interstellar Era
The Silent Citadel was the final Citadel constructed by the ADJM during the Interstellar Conflict, primarily suited towards Prototype Garrisai testing. As such, it was built far from the heat of battle, similar to the likes of Fort Hummingbird, with combat capabilities being second to none. Being built so late in the war, it primarily tested the final few AEGIS Program machines such as the Saturn and Jupiter.

Pre-Uprising Era
After the events of DUALITY, the DTRO tried their best to cover up the atrocities committed during the Nightwatch Incident, effectively deleting it from the history of Decholon. Following the defeat of the Dark Pegasus, it, alongside the Kingship and Dreadnought, had their remains gathered and transferred to the relatively remote Silent Citadel for storage. Despite the looming threat of the Second Armeli Invasion over Decholon's head, the DTRO still persisted on keeping the three machines involved away from active duty. With the secret still needing to be kept, the Citadel they were housed in was promptly vacated, and its resources distributed to other Citadels to fuel the front lines.

Alternatively, the Kingship and Dreadnought were both sent out to counter the Second Armeli Invasion, however this act would only be futile. The loss of troops, withdrawal of allied companies, as well as the focus on hiding the events of the Nightwatch Incident were what put the NDRC at a disadvantage. Both of the aforementioned machines had only been stabilized for a few days before promptly heading back out with otherwise lackluster equipment. Thus, both would be severely damaged and relocated to the Silent Citadel.

Constructed in the outlands of Cassiopeia, it was incredibly hard to find to begin with, thus reducing the likeliness for it to be raided. However, it was not enough to stop the Mercury Legion from stealing the LESLIE System and Urban Dreadnought shortly after their takeover and subsequent looting spree of Decholon. The remaining technology in the Citadel was left alone afterwards due to the Legion's need to focus on the UNI threat. However, the Citadel would continue to remain under Mercury Legion territories for a majority of the Harbinger Uprising.

Uprising Era
When the combined forces of the Minerva, Neptune, and Desperado Storm Remnants took over Midnight Base, the Silent Citadel was found not too long after. It was discovered from the coordinates listed in the archives of Midnight Base. It formerly housed the three machines and their corresponding equipment, though all that remained was the Kingship at 80% of its power, as well as the Pegasus which was locked down with steel restraints on all of its limbs, with its equipment having been stolen over the years (see the Zephyr FC, Firestorm, Archangel, and Alpha Predator).

The Kingship was slowly restored and repaired under its original pilot, John Orion, while the Pegasus was stolen by Dominic Ramirez after he heeded the call of the AI DESTINY_RUNNER. The conclusion of the Harbinger Uprising saw the Silent Citadel being put back into action as a military reserve storage unit, as the three units it was intended to seal away were all destroyed.

Trivia
- The Base's design was inspired from the Abandoned MKIII Shatterdome from the early stages of Harbinger 2584, and can be considered as its successor.

- Its name was inspired off of the Silent Cartographer from Halo: CE.