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- 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.
It can be assumed that, since it appears that CAMS is the only known settlement on planet, that the UNSC governs every action of the planet. This also means that the informal capital of the planet is CAMS. General Daniel Black is then the current leader of the planet, if this is the case.
Due to the nature of the planet, the UNSC presence on planet is quite high. There were ODSTs in orbit, ready to be launched if trouble arises. 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 this also the known head of the military, on planet.
Circinius IV was a very rural planet. There was a very temperate area as there was a large coniferous forest around CAMS. This region was also very mountainous having many hills and peaks. It is unknown if there was any terraforming done to the planet.
Currently, the only known settlement is the Corbulo Academy of Military Science campus. 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.
The planet was at least partially glassed after its discovery, causing huge forest fires.