- Main article: Battle of Circinius IV
The planet was invaded by the Covenant during a surprise attack on April 26, 2526 with the main battle taking place at the Corbulo Academy of Military Science and its surrounding forests. At least three Covenant Corvettes began the attack by destroying the space tether at CAMS, killing most of the people who were evacuating up the elevator and at its base. Ground forces arrived picking off people on campus. Almost everyone on the planet was killed during the invasion with the only known survivors of the attack being three remaining members of Hastati Squad; April Orenski, Michael Sullivan, and Thomas Lasky.
They were rescued by three members of Blue Team; SPARTAN-II Master Chief Petty Officer John-117, Petty Officer Second Class Kelly-087, and Lieutenant, Junior Grade Frederic-104 just as the Covenant were reaching their position with their glassing beams. At least five CCS-class battlecruisers were seen glassing the surface of the planet.
Like many other colonies, power was generated for CAMS through hydro-electricity and wind turbines. It also housed one of, if not the only, space tether.
Due to the nature of the planet, the UNSC presence on planet is quite high. ODSTs were in orbit at the time of the battle. As well, there was a complement of Marines to guard and defend the campus and restricted areas. Plus, there is the fact that every cadet on campus would in one way know how to operate UNSC weapons and would theoretically be just below in skill as a Marine. It was also seen that there were at least four Warthogs on campus. General Daniel Black was the head of the defenses at the school.
Circinius IV had large rural areas. This included a very temperate area with large coniferous forests around CAMS. This region was also very mountainous having many hills and peaks. It also had many bodies of water. It is unknown if there was any terraforming done to the planet.
The planet was at least partially glassed after its discovery, causing huge forest fires.
- Halo 4: Forward Unto Dawn (First appearance)
- Halo 4 (Mentioned only)
- Halo 2: Anniversary
- Outskirts (Mentioned only)