Citadel

"There was an illusion of safety, for a time. And then the Citadels appeared. It happened in a split second, all over the world. A chunk would disappear from the center of a city, to be replaced an instant later by one of these... headquarters for the Combine. Invasion Central."

- Eli Maxwell

The City 17 Citadel is one of the numerous Combine Citadels scattered around Earth. The most important, it houses the office of Earth Administrator Wallace Breen.

Overview


The Citadel was the massive structure from which the Combine govern the Earth. It was located in City 17, and resembled a massive, metallic skyscraper, rising several kilometers into the sky from ground level, and extending some distance underground as well. It is a triangular structure when viewed from above, and is crowned by a Dark Energy Reactor. Its associated portal is the primary means of communication with offworld Combine forces. The Citadel was heavily mechanized, and entire sections of it can move to allow for mass deployment of airborne Combine units such as scanners or hunter-choppers. It appears to either provide power to City 17 or drain power from it, as power lines can be seen extending out of it. Since the Citadel has its own massive reactor there is little reason or need to draw power from the city. These power lines then join on to regular transmission towers and poles, connecting it to the rest of the city.

The Citadel has two known "states," or configurations that the tower takes depending on specific situations. The first of these is what is most likely the dormant configuration, which is probably maintained during the majority of life in the city, when no serious threats are posed to the Combine (the structure also takes this shape during Half-Life 2: Episode One). This configuration is signified by a single set of rib-like structures exposed within the right half of the Citadel, with an outer metal plating retracted slightly above the inner plating. However, shortly after the player is transported inside Doctor Breen's office in the Citadel during the malfunctioning of Dr. Kleiner's teleporter, Breen puts the Citadel on alert, causing the structure to change to its alerted state. The Citadel can be seen changing its configuration while Barney Calhoun gives Gordon a crowbar. Barney says that this is a rare occasion, stating "I've never seen it lit up like that." The inner plating retracts upwards, exposing a total of four sets of "ribs", at the start of "Route Kanal", where the reconfiguration has fully completed. During this transformation a loud alarm resonates, echoing for several seconds each time it sounds, possibly emenating from the Citadel itself. A small piece of plating barely visible on the left (southern) side of the Citadel also descends partly down the tower, scanners rapidly deploy from that piece like dust, and the Citadel remains in this configuration for the remainder of the game. When Freeman sabotages the reactor, the plating descends to the "all clear" state and covers the ribs. The lower set of ribs descends along the tower and locks in place behind the lowest panel on the right hand side of the structure.It can be theorized that there are other configurations the Citadel may take in different situations, but these two are the only configurations depicted in the game.

As mentioned in the Raising the Bar book, entire blocks from City 17 vanished into thin air as the Combine delivered the Citadel to Earth. There is a slight mention of this event in Dr. Breen's first speech in Half-Life 2, during which he states that the Citadel was "thoughtfully provided by Our Benefactors." The Citadel is embedded in a huge chasm with antiquated aqueducts and newer sewer pipes with broken ends extending in from the walls of the pit and cars, now scrap metal, lying at the bottom of the pit: making it seem as if the Citadel plummeted into the ground forcefully from a high distance, and is completely surrounded by enormous mobile walls which chew up material around the Citadel and prevent access from the streets. Attached to the base of the Citadel are other machines that pound the ground. These are theorized to be used for destroying the city, acting as giant thumpers to repel Antlions (supported by the antlions that invaded the city after the Citadel's deactivation in Half-Life 2: Episode One), or gathering raw materials from the city's structures, but their true purpose remains unknown. It should be noted that the number of Citadels in Earth remains unknown in game. It also is clearly visible that there are numerous other Citadels outside Earth, as seen through an off-world portal which Dr. Breen intends to enter during the final moments of Half-Life 2.

Lower levels
In the first few chapters of Half-Life 2: Episode One, the player is given a firsthand look at much of the lower levels of the Citadel. Whilst mostly looking very much the same as the rest of the Citadel, no war factories or synth manufacturing plants are located in this area of the structure. During this point in the game the Citadel can be seen as extremely unstable, with an orange glow sweeping through the structure in contrast to the blue it used to be when functional. Fires have spread across the structure and much debris from what's left of the upper levels is constantly falling down to the lower levels.

An emergency evacuation chamber is located in the lower levels of the Citadel. The room is significantly different from that of the rest of the Citadel, giving off an eerie red glow from hundreds of bright lights mounted on the walls in contrast to the blue and orange that characterises the Citadel at the time. The room seems to serve as an emergency evacuation chamber, allowing Combine Advisors to quickly escape in times where the Citadel is in peril. The Advisor Pods are located under the glass floor of the room and when preparing to dock they rise up and move through a tube before positioning themselves in a chute and moving upwards.

Toward the very bottom of the Citadel is its core which is only accessible via a lift that descends several dozen floors. The core chamber is protected by large blast doors carrying an insignia with the appearance of a stylized version of the international symbol for radioactivity. A large control room is situated overlooking the core with a central access lift leading down to its chamber, similar in design to the control room overlooking the Dark Fusion reactor at the opposite end of the structure. Three rooms are located across the chamber which are specifically designed to help stabilise the core in the event that its energy output becomes unstable. The machines in these rooms form a threefold containment system that ensures that the intensity of the dark energy reaction within the core stays within safe limits. Connected onto the core itself is a train station where it is likely that Razor Train cargo is emptied. This point in the Citadel lies approximately one kilometer below the surface and extends throughout City 17 and beyond.

Central levels


In the final chapters of Half-Life 2, the player is given an insight into the interior of the Citadel, which contrasts its featureless exterior. Abundances of Combine technology are found within the Citadel, ranging from countless generators and force fields, to matter disintegration fields, to elevators and platforms that defy gravity, to giant tubes that transport unknown fluids. The architecture of the Combine has its greatest presence in the Citadel. The entire building is constructed from the same blackish blue metal which all Combine structures are made from. All "visitors" routinely have weapons stripped using a confiscation field, presumably to avoid precisely the situation which occurs at the end of Half-Life 2 and reoccurs at the beginning of Episode One – ironically, because of the presence of a confiscation field. It is also possible that some related technology extends throughout the Citadel, as any weapons dropped on the ground disintegrate in the same manner as in the confiscation field. This is not a by product of energy Orbs or the Gravity Gun, as those weapons dropped by soldiers killed by Alyx Vance also disintegrate.

There are railway systems running throughout the Citadel that are used by Razor Trains to ship and deliver cargo. Much of this cargo consists of new Stalkers from Nova Prospekt. Stalkers are delivered in pods, and the Citadel includes a large transportation system for these pods. Tasks such as the operation of basic panels, or the repairing of damaged Combine equipment and units is done by Stalkers, under the constant supervision of Overwatch personnel or scanners

The Citadel is presumed to include large war factories, where Combine equipment, technology and weapons, as well as Synths are manufactured. Two types of Synth that were never encountered elsewhere during the game, the crab synth and the mortar synth, can be seen being transported around on conveyor belts, indicating that they are possibly manufactured in the Citadel, although this could only be a means of moving the synths throughout the large facility. The Citadel also provides a central hub for Overwatch soldiers (including Elites), who are present in overwhelming numbers, and is the launching point for gunships.

Upper levels


Before reaching the very top of the citadel, Freeman passes through many open areas of the citadel where enormous segments of the citadel exterior wall open and close to allow dropships and gunships to quickly exit and enter the citadel's interior.

On one of the very top levels of the Citadel is Doctor Breen's office, believed to be the location from which he transmits his Breencasts-though the walls do not match his "studio" backdrop, suggesting there is a separate room for that purpose. Unlike the rest of the Citadel, Breen's office has a more classical, human look to it, although Combine architecture is still a very dominating feature in the room. His office includes various luxury items such as a wooden desk, mantle clock, leather seat, globe, expensive carpeting, and busts of himself, much like the generator rooms in the Overwatch nexus. His office also contains a large set of monitors, which act as his personal computer, and from which he can communicate with contacts such as the Combine Advisor. Breen's office is connected to the prisoner transport system used by Gordon Freeman, and there are many other prisoner pods around his office. Otherwise, more welcome guests can access the office via an elevator connected to the dark fusion reactor or a separate door from the prisoner entrance. It can be assumed that Breen lives in the Citadel as well as works in it.

The very top of the Citadel contains the Combine's dark fusion reactor-that seems to be directly connected to Breen's office, which is used to power their tunneling entanglement device and allow them to tunnel into Earth from their universe. At the end of Half-Life 2, Gordon manages to destabilize and destroy the dark fusion reactor using energy orbs.

Destruction


In Episode One, the aftermath of Gordon's assault on the Citadel is clearly visible. The overloading of the Dark Fusion reactor has downed power and destabilized the structure of the whole building, and Gordon must make his way to the core to re-engage the containment field and delay the core's inevitable meltdown. The Citadel is by this time barely occupied compared to its earlier state, presumably most of the soldiers and synths have been evacuated into City 17 to prevent the Citizens from escaping the blast. There are however, several soldiers left, and a few Stalkers for operating machinery. The Citadel's interior now glows orange, in stark contrast to the cold blue it used to be when functional, while bridges are falling apart and debris continuously falls from the top of the tower. From the outside, the Citadel's peak is surrounded by swirling black and red clouds with green lightning bolts emerging. The power lines connecting the Citadel to City 17 are no longer present, and the explosion of the Dark Fusion reactor has blown the top of the Citadel off. The climax of Episode One is witnessed by Gordon and Alyx, when the Citadel's core suffers the inevitable meltdown as it collects the colossal amount of energy needed to send a final data transmission off-world to the rest of the Combine empire.

In Half-Life 2: Episode Two, the Citadel still dominates City 17 even in its ruin. A superportal looms over the crater where the Citadel once stood, drawing power to open from the remnants of the dark fusion core through a swirling blue tendril of energy. At the end of Episode 2 the Citadel collapsed remains are all that is left of the once tall and overpowering structure.

Design evolution
The Citadel went through various designs during the game's development, as seen in several concept art images and the WC mappack. It started as a brush until becoming the model seen in Half-Life 2.

Organic version
This version has organic roots. It is featured in concept arts by Viktor Antonov and Dhabih Eng.

Rusty metal/concrete version
This version covers inside maps consisting in concrete and rusty metal, last edited in 2001. It is unsure which version they are from. They suggest the Citadel Core was originally to appear in Half-Life 2.

Tiles version

 * Designed by Viktor Antonov, this version is the last known brush version. It appears as a long cylinder divided in several parts and with other shapes stuck around it, where rooms and corridors can be found. Covered by grey and brown in the outside, it is topped by some kind of huge antenna. It is featured in the maps " ", " " (as a human-size version), " ", among others, most of them last edited in 2001.
 * It is also the first version featuring inside maps. Some shapes are similar to the retail version, except all floors, walls and ceilings are entirely covered in tiles. Metallic pipes with organic forms can also be found all around, as long with a prototype prison area with Citizens and Vortigaunts in the cells, having concept art for the Depot based on them. It should be noted that most of these maps are demos and prototypes and that they are very incomplete.
 * The shaft seen in the Citadel in Episode One where the Advisor leaves was originally to be seen in Half-Life 2 and is present as a prototype map (" ") in that Citadel version.
 * Most of the WC mappack inside maps are located in that version and were made by Randy Lundeen, according to the folder name, "randy". He also designed the cut propaganda posters featuring another Citadel version.

"Clamp" version
This version looks like a giant blue-grey clamp, with Depot-like buildings at its feet. It can be found in the map " ", last edited December 2002. According to one piece of concept art, it was likely designed by Viktor Antonov.

Poster version
This version is featured in the map " ", last edited December 2002. It is entirely brown and apparently not detailed, while a closer look shows it is, featuring a circle, windows and other precise shapes. It is featured in three Combine propaganda posters made by Randy Lundeen (who mapped the tiles version of the citadel) and based on artwork by Dhabih Eng. In its skybox can be found the "inner wall" mentioned by Alyx in the playable Half-Life 2 Beta sound files, and where Vance Headquarters are located, as well as the radio tower located near the Manhack Arcade and Kleiner's Lab.

E3 Terminal version
The version, the first model, is a round and blueish version. It is featured in the latest version of the map " ".

Retail version
The last version and second model, designed by Jeff Ballinger and Viktor Antonov and featured in the playable Half-Life 2 Beta, is almost identical to the next and latest version. The next and last version, and the third model, is seen in Half-Life 2 is therefore. Almost identical to the previous version, it is more blue and more detailed.

Miscellaneous



 * Some designs were also taken from the Half-Life chapter Interloper, especially in the dark fusion reactor.
 * The current design bears an uncanny resemblance, intended or not, with the Bayonets Memorial in Zelenograd, Russia.
 * The Citadel was originally to feature a garbage incinerator, although it is not clear in what version of the Citadel it was to be located.

List of appearances

 * Half-Life 2
 * Half-Life 2: Raising the Bar
 * Half-Life 2: Episode One
 * Half-Life 2: Episode Two