Halo Array

The Halo Array was a collection of gigantic Fortress Worlds built by the Forerunners to cleanse the Galaxy of the Flood by killing everything on every planet that they knew of. Smart.

There were originally twelve Halo rings, but in-fighting and changing of ideals meant that five of the rings were lost forever. The lack of Halo rings meant that the cleansing could only cover the initial Galaxy, not the whole universe as the idiotic Forerunners had planned.

The Didact had plans to render the Galaxy lifeless, but a change of heart by the Librarian meant that the Ark was built to contain specimins of species from all over the Galaxy, meaning that they could be saved. Although thi seemed like a spark of hidden Forerunner intelligence, it was actually 007 Greenie Spark who was responsible for this idea.

Each Ring had a Monitor, designated with caretaking and managing the ring during its existance and defending it if necessary. The rings also had Sentinels to defend it from attack and Constructors to repair it if it is damaged.

Halo Rings
Note: The rings here are the original twelve, and those that remained after the Monitor Civil War are shown with their new, re-ordered designations. They are also shown with the name of their Monitor, if it is known.
 * Installation 01, Monitor 007 Greenie Spark.
 * Installation 02 - Halo Installation 05, Monitor 2401 Penitent Tangent
 * Installation 03 - Halo Installation 01
 * Installation 04 - Halo Installation 06
 * Installation 05 - Halo Installation 07
 * Installation 06
 * Installation 07
 * Installation 08
 * Installation 09
 * Installation 10 - Halo Installation 02, Monitor 686 Pessimistic Insight
 * Installation 11 - Halo Installation 03, Monitor 049 Abject Testament
 * Installation 12 - Halo Installation 04, Monitor 343 Guilty Spark

The Ark
The Ark, aka Installation 00, was created after the departure of the five rebel Halos around a pre-existing Forerunner structure known as the Foundry. The Foundry was the device used by Forerunners to build new Halos, and it is ironic that the Ark was built around this tool of destruction since the Ark itself has a purpose that is purely peaceful. The Ark was created by the Librarian, after being 'suggested' by 007 Greenie Spark, to contain samples of all the species that the Halo rings would destroy, which would allow them to be re-seeded back tot heir corresponding planets.

The Ark was critically damaged during a battle between the Human-Covenent Seperatist Alliance, the Covenant Loyalists and the Flood. However, it slowly repaired itself and, using materials that would have been used to replace the devastated Installation 02, the Ark soon reconstructed itself to its former glory. Not only that, but Low Charity left the Ark with Gravemind aboard, ready to continue his new life of peace. So the Ark did fulfil its final purpose - it destroyed the Flood, saved the Galaxy and brought peace to its inhabitants.