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NOTE: This article contains endgame spoilers. Read further at your own peril.

Cydonia is the generally-accepted name for the final mission of UFO: Enemy Unknown, in which X-Com assaults the alien menace at its source. A great deal of research is required to discover Cydonia, a great deal of engineering is required to reach it, and (naturally) a great deal of skill is required to assault it. Completing the mission wins the game; conversely, a failed assault on Cydonia loses the game.

The mission itself comes in two parts: "Mars: Cydonia Landing" and "Mars: The Final Assault". Each part has its own map, populated with different enemies; the crew you bring must complete both parts in sequence. But before that, of course, you must unlock the mission.

Getting to Cydonia

Cydonia or Bust

To assault the alien base at Cydonia, one must first know that there is an alien base at Cydonia. The path to find this out begins when X-Com interrogates a live alien, unlocking the research topic Alien Origins, which reveals that the hordes of UFOs assaulting Earth have a staging point somewhere in the Solar System. After this, interrogating an alien Leader (or Commander) will unlock the topic The Martian Solution, which establishes that this base is on Mars. Then, when an alien Commander is interrogated, Cydonia or Bust is unlocked, which gives the exact location of the alien stronghold - Cydonia. With this information, X-Com gains the ability to launch an attack on Cydonia and end the alien threat once and for all... assuming they have some way to get there.

The Ultimate Craft

One cannot simply fly a Skyranger to Mars. To reach Cydonia, X-Com must design a space-capable troop transporter. X-Com must first research the four key components of any UFO - Alien Alloys, Elerium-115, UFO Power Sources and UFO Navigation, unlocking the topic UFO Construction which leads to a series of craft. The last of the series, the Avenger, is capable of flying to Cydonia, and (provided Cydonia or Bust has been researched), a button labelled "Cydonia" will appear when choosing an Avenger's destination.

Shopping list

The above two items - an Avenger and researching Cydonia or Bust - are technically the only requirements to assault Cydonia. However, as the mission is far harder than any other in UFO: Enemy Unknown, and a failed Cydonia assault results in losing the game, it is wise to prepare rather more extensively. Below is a list of things you may wish to acquire before making the attempt.

  • Armour, preferably Flying Suits. By the time you get to Cydonia the aliens will largely be using Heavy Plasma, but any chance of avoiding death is better than none. Flying Suits are the best protection available, although their flight capability isn't as useful in the second half (due to the enclosed space).
    • Medi-Kits. The mission can be very long, and as such wounded soldiers will often die of their wounds if not treated.
  • Heavy Plasma. Cydonia contains many heavily armoured aliens, so you'll want the biggest guns available. Some prefer to bring Laser Rifles with the squad (to save items) and take Heavy Plasma Guns from the dead fingers of the Sectoids in the first half of the mission, but you will at least need to have researched the weapon to use it. Bringing reloads is usually superfluous due to the aforementioned ability to loot aliens' corpses.
  • Hovertanks, especially Hovertanks/Launcher. Hovertanks are fast and well-armoured, and the Hovertank/Launcher's ability to defeat a Sectopod toe-to-toe is not to be underestimated. The more powerful man-portable Blaster Launcher is also an option, but it strains your item limit, requires reloading after every shot, and may end up being used against you.
  • Electro-flares or an Auto-Cannon loaded with Incendiary rounds. It's dark on Mars, so illumination is helpful. Incendiaries use less of your precious 80 items, but fire doesn't last very long.
  • And last, but certainly not least: Psionics. There are many, many psionic aliens in Cydonia, and as such soldiers with low Psi-Strength will spend nearly all of their time under alien mind control. Offensive psionics (soldiers with high Psi-Skill armed with Psi-Amps) help a lot but aren't essential; winnowing your troops by Psi-Strength, however, is all-but-required to reduce the number of successful psi attacks to something manageable.

Mars: Cydonia Landing


Your Avenger craft has landed in the region of Cydonia on the surface of Mars. Our information indicates that one of the pyramid constructions contains a green access lift to an underground complex. Once you have assembled all your soldiers in the lift area, continue to the next stage…


This first part of the mission is similar to a UFO recovery or terror mission; an outdoor map with your troops starting in the Avenger, and small buildings dotting the map. In this case, however, the terrain is that of Mars' cratered surface, and the buildings are alien pyramids. The map is 50x50.

Opposition consists of Sectoids and Cyberdiscs, in numbers similar to those encountered on board a Terror ship. However, far more of the Sectoids will be psionically active than in such a mission. Note also that it is considered dark on Mars regardless of the time you launched the Avenger (normal rules for Night Missions apply).

There are two ways to clear this map; you must either find the unique pyramid with a lift down to the base proper (green floor tiles in the interior), climb inside and abort the mission (transferring all soldiers, tanks and equipment on said lift to the second part), or simply kill all the aliens (transferring all soldiers, tanks and held equipment to the second part wherever they are).

PC version sample Cydonia Landing Layout

Cydonia Landing in PC version

A random sample of the Cydonia Landing in Mars from PC version the game.

Alien deployment (surface)

Rank Beg./Exp. Vet./Gen. Super.
Sectoid Soldiers456
Sectoid Navigators000
Sectoid Medics000
Sectoid Engineers000
Sectoid Leaders345
Sectoid Commanders345


  • The doors of the pyramid containing the lift are only 1 tile wide, so Heavy Weapons Platforms will not fit. If you wish to take HWPs into the second half of the mission, you must either widen the door with a Heavy Plasma Gun or Blaster Launcher, or complete the map by killing all the aliens.
  • In defiance of currently-understood biology, your soldiers will not suffocate on Mars; while Power Suits or Flying Suits are recommended, your troops can survive without helmeted attire. Likewise, throwing distances are unaffected by Mars' lower gravity.
  • While only one pyramid contains the lift to the base, all the pyramids can be entered, and many will contain aliens. Craters can also conceal aliens.
  • Loot dead Sectoids for spare clips as you pass by them; the hardest battle still lies ahead.

Mars: The Final Assault


The pyramid lift takes your battle weary soldiers deep below the planet's surface. They arrive in the heart of a large complex of tunnels and chambers. The alien brain is hidden somewhere in the labyrinth. It must be destroyed if the earth is to be saved from alien enslavement.

Good Luck!


The Alien Brain

The second half of the mission is very similar to an Alien Base Assault, with X-Com's remaining soldiers and tanks spawning in entry modules and having to navigate through a darkened maze filled with aliens. However, there are several important differences, nearly all of them bad for X-Com.

  • The map is larger; instead of a 50x50 map, the base in Cydonia is 60x60 (like a Base Defence).
  • The Ethereal crew is supported not only by their usual Sectopods, but also by Silacoids, Celatids and the dreaded Chryssalids.
  • Instead of a normal base command centre, the base at Cydonia has a unique module containing the Alien Brain (pictured at right). To win the mission - and the game - X-Com must destroy at least one segment of the four-tile Brain (which has 40 tile armour). The Brain is guarded by several Ethereal Commanders.

Note that, regardless of how long the war has gone on, the Ethereals at Cydonia will always be equipped with endgame weaponry - Heavy Plasma Guns and Blaster Launchers.

PC version random layout

A possible Cydonia base in PC version

A random sample of the Cydonia base map from the PC version.

PSX version layout

The underground Cydonia base in the Playstation version of the game.

Unlike in the PC versions of the game - which have a randomly generated base - the base in the Playstation version always has the same layout (see pic to the right). This has the important implication that you will always know the location of the Brain Room.

Alien deployment (underground base)

Rank Beg./Exp. Vet./Gen. Super.
Ethereal Soldiers234
Ethereal Leaders123
Ethereal Commanders345

As this is the first time in X-COM which has a "mixed" mission, the programmers didn't quite get the substitutions correct per se. The proper aliens and ranks show up, but substitution was used in some instances where it wasn't necessary. For instance, instead of just spawning Ethereal commanders normally, the programmers substituted commanders for the missing engineer rank and instead of spawning Ethereal soldiers normally they substituted them in lieu of commanders.

Rank Value Normal Rank Cydonia Rank
7Terrorist #1Sectopod


  • As Ethereals don't appear on Earth very often (almost never before July), the battle at Cydonia may be the first (and only) time you encounter them. The short version is that they're midway between Snakemen and Mutons in durability, but have exceptionally-high Reactions, Firing Accuracy and Time Units; assume that any soldier performing a reaction-fire trigger will get shot. Worse, every Ethereal is capable of using Psionics to panic or mind-control your soldiers.
  • The Ethereal terror unit, the Sectopod, is equally terrifying. Like Cyberdiscs, Sectopods are large, robotic units with built-in energy weaponry. While they cannot fly like Cyberdiscs, Sectopods more than make up for it with their extreme durability on difficulties above Beginner; the otherwise-superlative Heavy Plasma Gun, for instance, only has a 20% chance to inflict any damage whatsoever to a Sectopod's front armour, and will usually take over a dozen hits to destroy a Sectopod outright. The only weapons that can be considered truly effective against Sectopods are the man-portable Blaster Launcher and Small Launcher and the Hovertank/Launcher heavy weapons platform; the Heavy Laser is of some use due to Sectopods' weakness to Laser damage but is rather inaccurate and slow.
  • Between mind-controlling Ethereals equipped with Blaster Launchers, nigh-indestructible Sectopods, and deadly Chryssalids, the odds are heavily stacked against X-Com's squad. Forget about killing all the aliens (on Superhuman, there are over thirty); your objective is to find and destroy the Brain before your soldiers are wiped out.
  • The Brain Room is a large (20x20) module walled with ordinary UFO bulkhead material (not the "security walls" with crown molding), with a "security" door (dark grey) on the west side (upper-left in the isometric view). Don't confuse it with a storage compartment, which has "security" walls and has a normal door on the south (lower-left) side.
  • Once through the door of the module, you'll find a long corridor terminating in a pair of one-square lifts into the Brain Room proper. Unfortunately, there are between three and five (depending on difficulty) Ethereal Commanders guarding the upper level, and they will not hesitate to mind-control your soldiers as they walk directly underneath them, or mow them down with Heavy Plasma reaction fire as they ascend the lifts. There are several ways to overcome this deathtrap:
    • Most obviously, you can simply send a large (8+) group of heavily-armed, very psi-resistant soldiers in and make them all go up the lifts in a single turn. The Ethereals will run out of Time Units eventually, and then you can slaughter them or shoot the Brain directly.
    • You can use the Blaster Launcher to dig a new tunnel through the wall of the upper level (you need a full-strength Blaster Bomb to remove the dirt wall, and before that you need to remove the metal covering with either massed Heavy Plasma fire or another Blaster Bomb). The best spot is in the NE corner of the module to the WSW, as this opens up directly behind the Brain with the Brain itself providing cover from the Ethereals and a relatively-easy shot for either a soldier in a Flying Suit or another Blaster Bomb/HWP Fusion Bomb. You could also send a Blaster Bomb or HWP Fusion Bomb up the lift, as long as you're playing the DOS version (it may hit an Ethereal, but the splash damage will probably write off the Brain anyway, and in any case the Ethereals being killed lets you send soldiers up the lifts to finish the job).
    • If you have highly skilled psionic soldiers of your own, then once you spot one of the Ethereals (even by looking up the lift, which usually won't give you a line of fire), you can mind-control them into shooting each other or the Brain.
    • Or you could cut through the floor under the Brain with Heavy Plasma fire and destroy it from underneath (it's directly above the first 4 squares inside the module door). More dubiously, a collision detection exploit allows explosive weapons fired into the ceiling to phase through it and hit the Brain directly.
  • The Alien Brain is an object with 40 armour. Most weapons deal 25%-75% of their listed damage to terrain, while explosives deal a fixed 50%. Thus, any impact-damage weapon with 54 or more listed damage (Heavy Cannon AP rounds, and all the two-handed energy weapons) has at least some chance of destroying the Brain, but only the Heavy Plasma Gun will do it reliably (i.e. if you're not using Heavy Plasma, kill the Ethereals first and then start blasting the Brain). Any explosive with 80 or more listed damage (Tank/Rocket Launcher, Large Rockets, High Explosive, as well as any alien-derived explosive) is guaranteed to destroy the Brain on a direct hit.
    • Note that the "has the brain been damaged" flag (which causes you to win at the end of the turn) is not saved in a savegame. So if you obliterate the Brain and then save and reload, you are doomed.
  • Do not depend on a few "decoys" (unarmed soldiers with abysmal Psionic Strength, who are prioritised for alien psi-attacks but harmless if mind-controlled) to protect you fully from the Ethereals' psionics. As mentioned above, every single one of the Ethereals (between 6 and 12 depending on difficulty) is psionically active; on Superhuman, you're likely to face about a dozen psionic attacks per turn, which is enough to mind-control the decoys and still have plenty left to cause havoc.
  • Besides the Brain Room, there are a couple of other modules in Cydonia which don't appear in Earthly Alien Base Assaults. The most notable is a module that appears to be a dead end, with the corridors going into it simply terminating at a wall. However, there is no roof over the "dead end", so any unit capable of flight can navigate through the module by simply flying over the walls.

See also

UFO Badge X-COM: Enemy Unknown/UFO Defense
Mission Types:Crashed UFOLanded UFOTerror SiteAlien BaseBase DefenceCydonia