Halo (megastructure)

Halos are fictional megastructures and superweapons in the Halo video game series. 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 Halo's fiction, the Forerunners built the rings to contain and study the Flood, an infectious alien parasite. The rings also 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.

The Halos are massive ringworlds, which feature their own wildlife and weather. The constructs resemble Larry Niven's Ringworld concept in shape and design. The structure that Halo: Combat Evolved takes place on was initially to be a hollowed-out planet, but was changed to its ring design later in development; a staff member provided "Halo" as the name for both the ring and the video game after names such as Red Shift were suggested.