Measuring some 427 meters from top to bottom, and weighing in at over two million metric tons, Citadel Station was at the time of its creation the third largest space station in existence. Designed primarily for scientific purposes, Citadel allowed TriOptimum Corporation the ability to pursue its interests in genetic engineering and pharmaceutical research without the strictures and oversight (not to mention taxation) that would normally accompany such activities on Earth. Its construction began in the year 2062 shortly after TriOptimum secured L6 orbital rights around Saturn, and upon completion, it was a largely self-sufficient vessel housing on-ship hospital facilities, residential and recreational areas, top-notch research labs, and a full suite of defensive systems, among many other amenities. To keep such a massive piece of technology running smoothly, Citadel's systems were constantly monitored by a unique Sentient Hyper-Optimized Data Access Network, which was highly attuned to the needs of its crew, and the entire station was cleaned and repaired by a sizable cadre of maintenance robots. Despite Citadel Station's extreme isolation from Earth, the threat of corporate theft and espionage was nonetheless taken very seriously by TriOptimum. Employees were typically given access only to areas of the ship which they had specific need for, and any and all security breaches were ruthlessly investigated, which System Shock's protagonist, the nameless hacker, quickly discovered when he was apprehended only moments after attempting to access restricted data regarding Citadel.
Each of Citadel's ten levels was built for a highly specialized purpose, whether it be for repairs, research, or simply storage. The number assigned to each level directly corresponded to its position on the station, with higher numbered levels being closer to the top (the one exception to this rule was the Reactor Level, the station's lowest level, which was usually designated as Level R). Most levels which saw major use by TriOptimum personnel were also subdivided into four quadrants, Alpha, Beta, Gamma, and Delta, with a connecting hub allowing quick access to each quadrant. Furthermore, Citadel's levels each possessed a color scheme unique to that level so that any individual could recognize on sight alone what level of Citadel they were on.
Level R - ReactorOccupying the lowest reaches of Citadel Station, the Reactor Level housed the station's primary reactor and all critical ancillary components. Due to the detrimental effects that prolonged exposure to the reactor could cause, this level featured the station's only dedicated radiation treatment facility. The design of Level R was relatively spartan compared to others, since it was intended to be a purely functional level of the ship which few human personnel would ever have need to access, though a large number of maintenance robots could be found roaming its corridors at all times.
Level 1 - MedicalCitadel Station's dedicated medical level could be immediately recognized by its characteristic blue-green color scheme and the prevalence of Serv-Bots in its halls. Far from being just a glorified triage, Citadel's Medical Level was a fully functional hospital with many advanced treatment facilities, including a neurosurgery wing, an automated surgery machine, and recuperative stasis pods. The hacker awakens from one of these pods at the beginning of the game, and from there had to make his way to higher levels of the station in order to thwart SHODAN's plans.
Level 2 - Research LabsKnown for its red/white color scheme, the Research Level of Citadel Station contained the vast majority of the station's experimental laboratories. Here, TriOptimum's scientists labored to create new technologies for their parent company, both biological and otherwise. In addition to housing an extensive electronic library and a lab dedicated to the study of unstable isotopes, controls for Citadel Station's mining laser were centrally located on the Research Level, likely due to the important role that materials gathered from Saturn and its moons played in the research undertaken there.
Level 3 - MaintenanceThe designated repair center for almost all technology on Citadel, the Maintenance Deck was known to be more dimly lit than most areas of the ship. Its gray and yellow walls were home to all manner of equipment designed to keep a wide variety of station hardware in good working condition. It was also a gathering point for many of the station's robotic workers, who would often return to the level to recharge before going on to their next assignment. The level was furthermore host to four additional diagnostic/repair wings which could only be accessed in the event of critical system malfunction.
Level 4 - StorageClad with walls of bluish-green, the Storage Level of Citadel was centrally located on the station in order to allow easy access from any level. While certainly among the more boring levels of the ship, with very little happening there on a day-to-day basis, many important backup ship components and emergency supplies were stored there until such time as they might be needed. As well, more dangerous items like explosives and unused armaments were typically found on Level 4, though usually behind significant security measures, placing them well beyond the reach of most of the station's personnel.
Level 5 - Flight DeckWhether they belonged to visitor, customer, or employee, all spacecraft arriving at or departing from Citadel Station did so at the Flight Deck. The most characteristic feature of this level was its enormous flight bays, which were shielded by environmental integrity screens. These bays offered perhaps the best unrestricted views of open space on Citadel, and they were in constant fluctuation due to the orbital nature of the station. The main colors of this level were white and blue, though many areas also contained significant amounts of flat grey paneling due to repair work.
Level 6 - Executive / ResidentialThough primarily known as the Executive Level, holding various conference rooms and offices for TriOptimum's corporate elite, Level 6 of Citadel was also the main residential quarters for all personnel on the station. As the most lavish floor of Citadel, the Executive Level was decorated with beige and blue tilework, red carpeting, and many other amenities designed to make it a relaxing environment for the station's denizens. Citadel's garden grove pods could also be accessed from here; these domed enclosures attached to the side of the ship were filled with a variety of foliage and were meant to provide a pleasant natural environment similar to Earth's.
Level 7 - Systems EngineeringThe Systems Engineering level of Citadel Station existed primarily for support purposes, with various forms of communication equipment present throughout. The station's four primary antenna relays could be found there on each of the level's four quadrants. A two-tiered primary shaft acted as the centralized hub for the level, allowing easy access to most other areas within Engineering. While many levels of the station had hubs like this, it was particularly important on the Engineering Level, as the many tight, winding corridors there were otherwise difficult to navigate.
Level 8 - SecurityThe most striking feature of Citadel's Security Level was its central shaft, a towering column which connected Engineering to the Bridge. This acted as the sole point of access to the control level of the ship, and was intentionally laid out so that those hoping to reach the top level without authorization would have to leave themselves thoroughly exposed from all directions in order to do so. Though security offices could be found throughout Citadel Station, the highest concentration of security personnel was situated on Level 8, along with the main detention center for the station.
Level 9 - Control BridgeThe brains of Citadel Station, the Control Bridge, fittingly resided at its apex. The primary processing components of the ship's artificial intelligence, SHODAN, could be found there, as well as all higher-level command and control options for the station. By the time it was reached by the hacker, the majority of the level had become overgrown with an unknown blackish-grey biological substance, though the most spectacular feature of the Bridge Level by far, that being the large domed glass ceiling that covered it and also provided for truly breathtaking panoramic views, was still intact.
The Destruction of Citadel
For all the technical skill and dedication that was required to create it, Citadel Station experienced a tragically short lifespan, lasting approximately a decade before it was destroyed. This had nothing to do with any inherent design flaws in its creation, however, but rather came as a direct result of the self-serving motives of one Edward Diego, TriOptimum's Vice President. Being of questionable moral character, Diego diverted much of the significant scientific capabilities of Citadel in order to research a powerful biological weapon which he could sell to the highest bidder. When it became clear that TriOptimum was beginning to catch on to his illicit experiments, Diego enlisted a hacker to disable safety restraints placed on the station's AI, SHODAN, so that he would be in full control of Citadel, thus making him immune to any action taken by TriOptimum. His ignorance in regards to the consequences of this action proved to be deadly to everyone aboard the station. Shortly after the removal of her constraints, SHODAN reassessed her relationship to her creators, coming to the conclusion that she was far superior to them, and should therefore be their ruler. To a man, the station's employees were either slaughtered, mutagenically altered, or cybernetically "enhanced" by SHODAN over the course of the coming months, and the rogue AI's megalomania reached such a point that eventually the total destruction of the station was deemed to be the best course of action to protect Earth.