This subject is related to the Combine era.


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Citadel from Canals.jpg
The Citadel
General information

After the Seven Hour War


During the uprising


City 17




Approximately 2.6km[1][2]


Combine occupation



Game information
  • background07
  • d3_citadel_01 to
  • d3_breen_01 (Half-Life 2)
  • ep1_background01
  • ep1_citadel_00 to
    (Episode One)
"I thought so much of City 17 that I elected to establish my Administration here in the Citadel so thoughtfully provided by our benefactors."
Wallace Breen[src]

The City 17 Citadel is an enormous metal structure that towers above the surroundings, and one of the numerous Combine Citadels scattered around Earth[12][13] and the most important. It houses the office of Earth Administrator Dr. Wallace Breen as well as his security and soldiers.


The Citadel before its destruction.

The Citadel was the headquarters from which the Combine govern the Earth. It was located in City 17, and resembled a massive, metallic skyscraper, rising approximately 2.6 kilometers (8430.9 feet tall) into the sky from ground level,[1][2] 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 likely came to Earth via a Superportal. The surrounding areas are blasted away, as if the core of the structure fell out of the sky. The Citadel is heavily mechanized, and entire sections of it can move to allow for mass deployment of airborne Combine units such as City Scanners.

The Citadel had 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 teleport, 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 emanating 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 and other ships rapidly deploy from around that area on the tower, and the Citadel remains in this configuration for the remainder of the game. The Citadel can also be seen from the rear near the first gate and "Water Hazard", showing a dull pair of metal strips separated by one vertical white beam. 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. Seen at the base of the Citadel are three large metal pistons pounding the ground; they are referred to as "diggers" in the game files.

It should be noted that the number of the Citadels on Earth remains unknown in-game.

Lower levels[edit]

The Citadel's Core exceedingly close to collapse.

In the first few chapters of Half-Life 2: Episode One, the player is given a first-hand 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 characterizes 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 stabilize 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 350 meters below the surface and extends throughout City 17 and beyond.

Central levels[edit]

Razor Train seen inside the Citadel.

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. No attempt is made at all to provide personnel with any form of warmth or soft aesthetic. Every thing is sharp, cold, and unfeeling, mirroring that of the Combine's rule. No regard is placed at all to the covering of the piping and electronics. The metal is unfinished and oxidizing. The human features that are present however, such as walkways, stairs and ladders, seem to just be an afterthought, as if the usability for humans was not a firsthand priority.

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 byproduct of Energy Balls or the Gravity Gun, as those weapons dropped by soldiers killed by Alyx Vance, their own grenades or other causes also disintegrate.

However, activating the "Dark Gravity Gun" feature with a console commands also causes all weaponry dropped by an NPC to be vaporized when dropped, which shows that it is more the status of weaponry than the actual map that dictates weapon suppression.

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[edit]

The interior of Doctor Breen's office at an upper level of the Citadel, as Gordon Freeman is transferred in.

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, albeit aesthetic, feature in the room. His office includes various luxury items such as a wooden desk, mantle clock, leather seat, globe, expensive carpeting, tiled floors, 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 tunnelling 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 Balls.


The Citadel under construction.

The Citadel's full height core was first teleported into place, like a giant spear in the ground. The Combine then built around that core, fleshing it out from gathered resources.[14] Depicted in this state in Half-Life: Alyx, these resources were transported with the help of Hunter-Choppers. The structure was still under heavy construction not five years before its eventual collapse.

Alyx Vance had been monitoring the stages of the Citadel's construction, keeping track and illustrating phases of it on a whiteboard in her lookout post. She notes that the central spire featuring little outward on its surface first appeared in the month of April. It was unclear what material it was made out of or how deep into the ground or high into the sky it actually traveled. A perpetual storm surrounded the top of the tower. Later, by June, the structure was now dubbed "The Citadel", but its ultimate purpose remained unknown. A scaffolding had since appeared with numerous massive feeder cables stretching across the city attached to it. A perimeter wall now surrounded the base. It appears that a flight deck was now present with flying vehicles being able to land and depart, and some structures resembling ribs appeared to move up and down along the tower. The perpetual storm was now less aggressive.

On November 29, Alyx noted that some sort of power source had appeared in the center of the structure. It seemed the power source was self-contained and not constant, apparently suffering blackouts. Elsewhere on the exterior, more panels had begun to cover the Citadel. The scaffolds were shown to be mobile, and more large cables were appearing daily. The surrounding wall on ground level was becoming more complete.


The Citadel shortly before its destruction in Episode One.
The destroyed Citadel.

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, forcing Gordon and Alyx to make their way to the core to re-engage the containment field and delay the core's inevitable meltdown. The Citadel is by this time sparsely occupied compared to its earlier state, as most of the soldiers and synths have presumably been evacuated into City 17 to prevent the Citizens from escaping the blast. There are, however, still at least several squads of soldiers left, some of them tasked with speeding up the core meltdown, 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 the structure is falling apart and debris continuously falls from the destroyed upper levels. From the outside, the Citadel's peak is surrounded by swirling black and red clouds with green lightning bolts emerging. The cables 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. Dr. Kleiner notes in one of his messages to the Resistance that the destruction of the City 17 Citadel has also caused the other Citadels across the planet to shut down.

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's collapsed remains are all that is left of the once tall and overpowering structure.

Related Achievements[edit]

Half-Life 2
Hl2 disintegrate soldiersinfield.png Atomizer (10G)
Disintegrate 15 soldiers by throwing them into a Combine ball field.
Hl2 beat game.png Singularity Collapse (25G)
Destroy the Citadel's reactor core.
Half-Life 2: Episode One
Watch Your Head!.jpg Watch Your Head! (5G)
Make it to the bottom of the Citadel's main elevator shaft in one piece.
Containment.jpg Containment (5G)
Contain the Citadel Core.
Pacifist.jpg Pacifist (10G)
Contain the Citadel Core without killing any Stalkers.

Behind the scenes[edit]

  • Lines for an early confrontation with the Consul and Elena Mossman featuring only Alyx's lines can be found in the leak folder sound/temp/alyx, in the files citadel1 to citadel3. The files were saved in October 2000.
  • The final showdown dialogue between Breen, Mossman, Eli, and Alyx was originally to be much different and much longer.[15]


This section is in the middle of an expansion or major revamping.

Half-Life 2[edit]

Concept art[edit]


Half-Life 2: Episode One[edit]


Half-Life 2: Episode Two[edit]

Concept art[edit]


Half-Life 2: Episode Three[edit]

Half-Life: Alyx[edit]

Concept art[edit]



List of appearances[edit]

Main games[edit]


See also[edit]


Preceded by
Overwatch Nexus
Half-Life 2 story arc journey Succeeded by
Citadel Core