The Halo Array is a group of fictional megastructures and superweapons in the Halo science-fiction franchise, consisting of ringworlds known as Halos built by a structure known as the Ark. They are referred to as "Installations" by their artificial intelligence caretakers, and were created by an ancient race known as the Forerunners. The series' alien antagonists, the Covenant, refer to the Halos as the "Sacred Rings", believing them to form part of a greater religious prophecy known as "The Great Journey". In the games' stories, the Forerunners built the Halo Array to contain and study the Flood, an infectious alien parasite. The rings act together as a weapon of last resort; when fired, they kill all sentient life in the galaxy capable of falling prey to the Flood, thereby starving the p