Halo rings are fictional megastructures and superweapons in the Halo video game series, giving its name. They are referred to as "Installations" by their AI monitors, and are collectively referred to as "the Array" by the installations' creators, the Forerunners. The series' alien antagonists, the Covenant, refer to the structures as the "Sacred Rings", believing them to form part of a greater religious prophecy known as "The Great Journey". According to Halos fiction, the Forerunners built the rings to contain and study the Flood, an infectious alien parasite. The rings act together as a weapon of last resort; when fired, the rings kill any sentient life capable of falling prey to the Flood, starving the parasite of its food. The installations are at the crux of the plot progression for the Halo series.