From Halopedia, the Halo wiki
Actium was founded by the Unified Earth Government in 2389 and colonized as an Inner Colony. Though the colony was comparatively smaller to the colonies in the Sol and Epsilon Eridani systems, Actium was still a strong, densely populated core world.
During the Human-Covenant War, Actium was discovered by the Covenant in May 2545 and the ensuing campaign lasted less than a month. The engagement ended in heavy losses among local United Nations Space Command defenses, and the complete destruction of the 53rd Armored Division, resulting in the world's inevitable glassing. Before that happened, however, Actium's defenders managed to inflict heavy casualties on the Covenant.
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