From Halopedia, the Halo wiki
The Forerunners populated the world of DM-3-1123 b in DM-3-1123. During the Forerunner-Flood war, the planet was attacked by the Flood. While a Forerunner naval group engaged a Flood fleet of 149 non-military vessels in the system, the Flood landed on DM-3-1123 b and infested it, and the Forerunner fleet was forced to bombard the planet to cauterize the Flood's spread. About 1.36 million of the 2.26 billion residents were evacuated from the planet.
List of appearances