Galactic sterilization/Flood containment and research
Date of construction:
Before c. 100,000 BCE
Date of destruction:
10,000 kilometres (6,200 mi)
318 kilometres (198 mi)
-23°C to 40°C (-9°F to 104°F) (controlled)
The Covenant reverentially described Installation 04 as either the First Holy Ring, the First Sacred Ring, or the Holy Temple. After its destruction at the end of the Battle of Installation 04, the Ark started to construct a replacement for Installation 04.
The purpose of Installation 04, along with its brethren, was to preclude and thwart the parasite forms known as the Flood from consuming all sentient life in the galaxy by destroying all sentient life to prevent eventual consumption. In the event of a Flood outbreak, one of the seven installations could be triggered (in turn triggering the remaining Halos) to annihilate all sentient life within 25,000 light years. In the event of an unexpected shutdown, all remaining rings would go into a "standby state", in which they could be fired at once from the Ark if need be.
The climate of Installation 04 was very similar to Earth's climate. There have been hurricanes over the oceans on the ring. The weather was, however, extremely unpredictable - rain and snowfall could occur at random, leading Cortana to wonder if the weather was intentionally irregular, or if it followed a pattern such as snow being deliberately made at the control room to slow the Flood.
Installation 04 orbited the massive gas giant Threshold, and was suspended in the Lagrange point between Threshold and its largest natural satellite, Basis. The installation had a 24-degree axial tilt from Threshold's orbital plane. Due to this, any given point on the surface of the ring received sunlight from the star Soell for half of the time it was on the sunny side of Threshold, and none when was on the dark side. This created a somewhat unusual day-night cycle for the ring, in which it was dark three-fourths of the time and had no sunrise or sunset similar to those of a planet.
With a diameter of 10,000km and a surface width of 318km, the ring has a surface area of 3,180,000km2.
 Ancient history
Installation 04 was built by the Forerunners over 100,000 years before the Battle of Installation 04.[note 1] When the IsoDidact activated the Array at the Forerunner-Flood war's conclusion, ending the centuries-long conflict, Installation 04 was the first to fire, followed shortly after by the other six Halo rings. Installation 04 lay dormant for a hundred thousand years, with 343 Guilty Spark and his Sentinels ready to keep the Flood confined in the Flood containment facilities and keeping the infrastructure of the Halo in perfect working order.
 Intermediate period
After eons of uneventful existence on Installation 04, 343 Guilty Spark eventually found himself bored. For his own amusement, Spark began an experiment in which he evacuated entire sections of the Installation into space; according to Spark, these were experiments to measure the geologic effects of exposure to the vacuum of space and the eventual biological recovery of the evacuated sections, in order to gain insight into emergency response scenarios.
Around 40,000 BCE, an unidentified alien vessel crash landed in Sector 1215. Sometime prior to the crash the ship started broadcasting a distress signal. After attempting to translate it, 04-343 Guilty Spark blocked the signal, as no communication revealing the location of any of the Halos was allowed. After no lifeforms exited for several days, Spark had a large sarcophagus constructed around the vessel.
Between the activation of the Array and the arrival of the UNSC and the Covenant, a number of space-faring species stumbled across the installation. Although they reportedly explored the facility and recorded their findings, all of these species eventually left without breaking containment.
 Discovery and destruction
- "Halo... It's finished."
"No, I think we're just getting started."
- —Cortana and John-117 after the destruction of Installation 04.
The Covenant discovered the location of Installation 04 after the Covenant Fleet of Particular Justice followed the UNSC Pillar of Autumn, which was fleeing from the Fall of Reach through slipspace. The Halos are deeply ingrained into the Covenant's religious dogma, but prior to this discovery they had never actually found one. Due to the Covenant's faster slipspace capabilities, they arrived before the Pillar of Autumn.
The Pillar of Autumn arrived around September 19, 2552 and was promptly shot down by the warding Covenant ships. Shortly thereafter, the Covenant ground forces on Installation 04 accidentally unleashed the Flood from captivity. Humans, Flood, and the Covenant fought massive battles against one another as the Forerunner constructs tried to control the outbreak by activating Halo. The ring's monitor, 343 Guilty Spark, tried to convince the Master Chief to activate Halo. Not knowing the truth of what it did, he attempted to light the ring but was stopped by his AI friend and companion Cortana who was in the Core. She informed the Master Chief of Halo's true purpose and stashed the Activation Index in her memory banks. The Monitor betrayed the two and tried to kill the Master Chief and retrieve Cortana, but the two escaped and started plotting against him. In the end, John-117 detonated the Pillar of Autumn's fusion reactors in order to destroy the ring. The detonation critically damaged the superstructure below it, causing the ring to splinter into pieces.
Only a handful of humans and Covenant survived the battle. 343 Guilty Spark floated through space to a gas mining platform over Threshold, where he stumbled upon a Covenant expeditionary force. Inspired by his words, they began a heretical rebellion against the greater Covenant. Installation 04's destruction is seen as the first step in the chain of events that led to the Great Schism. The Heretics were quelled by Arbiter Thel 'Vadam who silenced their leader, but the seeds of a rebellion were planted. The Monitor was then captured by the loyal Covenant and later defected to the humans' side until he was destroyed on the replacement Alpha Halo by Spartan-117 with the help of Sergeant Johnson.
Installation 04 was the first Halo installation encountered by humanity, as well as first to be destroyed. Its destruction triggered the activation of a portal leading to the Sharpened Shield on Onyx, and also caused the Ark to start constructing a replacement ring.
There is now a large field of debris where Installation 04 was, though a few large chunks of the ring remain. Some smaller pieces of the Installation 04 have landed on Basis, while others have burned up in Threshold's atmosphere upon entry.
Some Flood specimens survived the ringworld's destruction, and was eventually retrieved by the prison ship Mona Lisa, which has been converted to an ONI research vessel. The ship was promptly overrun, forcing the UNSC prowler Red Horse to destroy the vessel with a Shiva-class nuclear missile.
- Main article: Installation 04B
Shortly after the destruction of the Halo, Installation 00 began to automatically construct a new Halo to replace Installation 04. This exact copy of the first Halo ring was nearing completion only a few months after the first ring was destroyed, but was also subsequently destroyed when it was fired before it was ready by the John-117 and Cortana. 343 Guilty Spark attempted to prevent this, but was finally destroyed by the Master Chief with the help of Sergeant Johnson in this new ring's Control Room.
- Sergeant Johnson humorously describes Installation 04 as "God's own anti-son-of-a-bitch-machine" and a "giant hula-hoop".
- Except for Boarding Action and Chiron TL-34, all Halo: Combat Evolved multiplayer map are surely or possibly set on Installation 04.
- It is possible to see falling debris from Installation 04 on the Halo 2 multiplayer map Burial Mounds.
Concept art of Installation 04 in Halo: Combat Evolved Anniversary.
Installation 04 orbiting Threshold, as seen in Halo: Combat Evolved.
One of Installation 04's three phase pulse generators.
Installation 04, as seen in a Terminal.
 List of appearances
- Halo: Combat Evolved
- Halo 2
- Halo 3 (Mentioned only)
- Halo: Reach
- Halo: Combat Evolved Anniversary
- Halo: The Fall of Reach (First appearance)
- Halo: The Flood
- Halo: First Strike
- Halo: Ghosts of Onyx (Mentioned only)
- Halo: Evolutions - Essential Tales of the Halo Universe
- Halo Graphic Novel
- Halo Legends
- Halo: Fall of Reach
- Halo: Silentium
- ^ In Halo: The Flood, 343 Guilty Spark states that the ring was 101,217 years old in 2552. However, this was measured in the Soell system's local time.
- ^ a b c d e f g Halo: The Essential Visual Guide, page 6
- ^ Halo: The Flood, page 14
- ^ Halo: The Flood, page 107
- ^ Halo: Combat Evolved, campaign level Assault on the Control Room
- ^ Halo: Combat Evolved: Sybex Official Strategies & Secrets, page 64
- ^ Halo: The Flood, page 238
- ^ Halo: Silentium, String 38
- ^ Halo: Combat Evolved Anniversary - Terminal 4
- ^ a b Halo: Combat Evolved Anniversary - Terminal 5
- ^ a b Halo: Combat Evolved Anniversary - Terminal 6 (343 Guilty Spark: "I have now endured 60,000 years without word from outside the Array.")
- ^ Conversations from the Universe, 343 Guilty Spark's Log
- ^ Halo: Combat Evolved, campaign level The Maw
- ^ Halo 2, campaign level The Heretic
- ^ Halo 2, multiplayer map Burial Mounds
- ^ Halo: Evolution - Essential Tales of the Halo Universe, The Mona Lisa