From Halopedia, the Halo wiki
Algolis was a human colony planet. The planet possessed a single moon. Algolis housed a relatively small civilian population and was home to some of the Office of Naval Intelligence's research and development projects for prototype weapons, including the HRUNTING/YGGDRASIL Mark I ADS.
The Office of Naval Intelligence's Section Three had facilities on the planet, to which several SPARTAN-II augmentation chemical precursors were sent without Dr. Catherine Halsey's consent, likely in order to be researched for Project CHRYSANTHEMUM.
The colony was attacked by the Covenant at some time before March 28, 2549.[Note 1] During the battle, the planet's civilians were evacuated while Marines from the UNSC Marine Corps of Engineers made a last stand against Covenant forces. The UNSC destroyer UNSC Heart of Midlothian was en route to the planet to secure a powered armor before the facility was attacked. The planet's survivors escaped in transport ships to a UNSC frigate in orbit that carried them to safety. The battle also resulted in the formation of the Banished as well. Overall, it is unknown what happened to the colony following the battle.
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