
Built following the Human-Forerunner War, these ringworlds were later used as a last resort against the Flood, a parasitic extra-galactic species that threatened to consume every sentient life-form in the galaxy. Īs it is known in modern times, the Halo Array is a network of seven ring-shaped megastructures created by the Forerunners, designed to exterminate all sentient life within the Milky Way galaxy. The Librarian's studies also helped determine if the rings could be used to repopulate the galaxy as part of the Conservation Measure. The research on the animals would be more deeply analyzed if they did become infected. With the Master Builder's permission, the Librarian would research each animal to detect if their bodies reacted to Flood infection. The life forms that were hand-selected by the Librarian included marine life, fauna, and land vertebrates. In addition to serving as weapons of last resort, Halo installations are also research facilities dedicated to containing and studying many different kinds of life forms. All sentient beings in the galaxy were killed, robbing the Flood of hosts and starving it to death. Eventually, eleven were destroyed and/or lost while the remaining seven were used by the Forerunners as a last resort when combating the parasitic Flood. Later, the weapons would be refined further and a new array of six smaller and significantly more lethal installations was constructed the newer Halos are known as the "neoteric" rings. The first array of twelve Halos was constructed by order of Master Builder Faber circa 98,445 BCE with the intent of being an ultimate weapon, one that would secure the preeminence of the Builder rate in Forerunner society. The Halos were also referred to by the Covenant as the Sacred Rings, and labeled as Installations or infrequently referred to as Fortress Worlds by the Forerunners and their monitors. The Halo Array, sometimes known simply as Halo or the Array, is a network of colossal ring-shaped superweapons individually known as Halos or Halo rings, constructed by the Forerunners. And that's exactly what Halo is designed to do: wipe the galaxy clean of all sentient life!" - Cortana during the Battle of Installation 04.

" Halo doesn't kill Flood, it kills their food! Humans, Covenant, whatever-we're all equally edible! The only way to stop the Flood is to starve them to death. The Array at Installation 00, just before their departure to firing sites across the galaxy.
