The Halo Array is a system of colossal ring-shaped superweapons. Circa 97,445 seven Halo rings were used by the Forerunners as a last resort when combating the parasitic Flood. All sentient beings in the galaxy were killed, robbing the Flood of hosts and starving it to death. 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, including marine life, fauna, and land vertebrates.