For exactly 101 217 local years, it lay forgotten and derelict in a disused portion of space. Sedentary, save for the unrelenting pull of Basis and Threshold, Halo was a testament to its builders' technological capabilities. It was constructed to withstand innumerable millennia, and this superannuated edifice certainly shows that the Forerunner were very capable at their craft. So Installation 04 sat; a facility left derelict for eons by its makers, yet visited and documented by numerous races throughout its quiescent past. Not till recently, however, was its purpose dredged from its depths.
Upon return to Einsteinian space at the co-ordinates detailed upon the rune-etched rock of Sigma Octanus, Cortana and Jacob Keyes discovered the ring. Roughly 10,000 kilometres in diameter and 22.3 km thick, Halo remains in orbit at a Lagrange point between Basis, the moon, and Threshold, the gas giant (Earth Survey Catalogue Number B1008-AG). With the Pillar of Autumn immutably crippled and their defeat unavoidable, Keyes decided to abandon ship and take flight to Halo.
Halo's geography was much like they had hoped, but far from what they could have expected. It was Earth-like, complete with mountains, hills, plains, seas, rivers, waterfalls, swamps, deserts, and icy canyons, with the only surprise being just how multi-climatic it was, considering that Halo was artificial. At a cursory glance, it seemed to be little more than a large, and habitable, ring-shaped construct; a feat of engineering and will. But, as they delved further into the interiors of Halo, and as they continued to monitor Covenant transmissions, they began to suspect that Halo was more than a mere ecosystem. The almost termitic passageways and arcane machinery of the Forerunner were intricately woven throughout the entire Halo. And although Halo outwardly appeared to be benign, it's seemingly contradictory purpose was soon discovered.
When Cortana uploaded herself into Halo's network, she uncovered Halo's true use, which the Covenant had only had mild inferences of. Halo was designed to study, contain, and, if necessary, prevent the Flood from spreading throughout the galaxy. It was indeed a weapon, and although mysteriously not an all smiting cudgel, seemingly not one that could be accurately wielded by either Covenant, or Human, against each other. With a maximum range of 25,000 light years, Halo would easily destroy them both, and all other life capable of sustaining the Flood. What good it does to kill all life quickly before all life is merely consumed by the Flood eventually is known only to the builders. Susceptible life situated on the ring is also eliminated.
After Master Chief is made aware of Halo's true function, it is decided that this Halo should be destroyed to prevent 343 Guilty Spark from finding someone else to activate Halo at some point in the future. Amidst the Covenant cries of heresy, by blasting the vent core of the Pillar of Autumn, Master Chief and Cortana succeed in ending the threat of Alpha Halo 04. 1 down, 6 to go.
Another piece of the puzzle, Delta Halo 05 is the second of seven ancient ring facilities to be discovered by the Covenant and Humanity alike. Whether the Prophet of Regret retreated to it as an already known location, or recovered its coordinates from a builing/object on Earth is unknown. The ring appears to possess strikingly similar facility types and terrain to that of Halo 04, though the whirlwind tour of both makes the assertion somewhat difficult to confrim. Conjecture, as always, is welcome.
Une histoire complete sur les mysterieux Halo