Halo Installation 04

"Whoever controls Halo controls the fate of the universe."
— Captain Jacob Keyes

Installation 04, also known as Alpha Halo, or simply Halo,was one of seven ring-shaped superweapons that comprised the Forerunners' Halo Array. It was located in the Soell system in the Orion Arm and was the closest Halo ring to the human sphere.

From Halopedia, the Halo wiki