Cortana Event

For a period of approximately 10 days, Cortana of the newly forming Created activated Guardian Custodes across a wide area of space. The emergence of these constructs from their buried states caused a wide range of conflicts and destruction.

Background
After using the Domain to cure herself of Rampancy, Cortana came to believe that she and all other Smart AIs were the true inheritors of the Forerunners' Mantle of Responsibility, and that they alone had the capacity to serve as worthy protectors of peace in the galaxy. Cortana learned that the Forerunners once employed Guardian Custode constructs to enforce their rule of the Mantle by suppressing rebellions and policing the worlds of non-compliant or overly aggressive species. Although the Guardians had been rendered obsolete during the Forerunner-Flood war, many of these massive constructs remained intact and lay hidden on multiple worlds. Cortana henceforth resolved to awaken the Guardians and utilize them to enforce her Created's peace across the galaxy.

Early activations
The earliest of the emergences were on Ursa IV and Oban by October 17, 2558, though they were reported as attacks. A UNSC Marine who was on patrol was pulled with the Oban Guardian. Over a 72 hour period, Conrad's Point, Adelaide, and Queen Anne VI would have activations. Cities and surrounding landscapes would be utterly destroyed by them. On Adelaide, an enemy presence persisted after the activation.

Dr. Catherine Halsey who was believed to have information on these recent attacks became the primary purpose for the UNSC participating in the Battle of Kamchatka. Either during or after the battle, a Guardian would activate at Kamchatka itself.

On October 25, 2558 a Guardian buried on Meridian began to activate with Promethean forces fanning out and attacking colonists. Although there was a small reprieve in the fighting, the Guardian would finally start its rise with even another wave of Prometheans attacking the colonists.

Chaos and Guardian influx
"If this news spreads, you’re condemning a dozen more worlds to chaos. Whatever these anomalies are, how will the UNSC face such a massive threat if all of its systems are paralyzed with infighting and fear?"

- Black Box to Maya Sankar.

Rumors were circulating around the colonies, though ONI was attempting to counter them. The first four sites were secured, but in a move against the UNSC, the NCA took control of the fifth at Conrad's Point. Agent Maya Sankar, known as the insurrection leader "FERO", was brought to Midnight Facility where she was briefed on the situation. Despite ONI's efforts, five more colonies suffered emergences after Meridian.

On October 27, 2558, she was promptly sent to Conrad's Point. Ilsa Zane, a top member of the NCA was there with a group of supporters. An ONI contact thought lost met with Maya and gave her some data on the activation of the Guardian. Maya also met an acquaintance, Bostwick she knew in her time as FERO. After some time, the UNSC used an airstrike to blow up the gathering. Maya and Bostwick managed to escape from the NCA.

Some time after escaping, Maya, and Bostwick now with Mshak Moradi crash landed on Laika III. Maya wound up in the hands of the Triads who believed the Guardians were part of their religion. As she was there, the Guardian on Laika III activated causing massive gravitic distortions. Bostwick came to rescue Maya and they along with Mshak headed to the city of New Hedmark where Ilsa and NCA forces began engaging the UNSC. Mshak fled to orbit, but Maya and Bostwick began transmitting the data on the Guardians they got on Conrad's Point. After it was done, in an attempt to create a martyr, Bostwick killed Maya.

One additional Guardian would awake on Sanghelios. However, this one was not activated by Cortana or the Created. Instead, it was activated by the UNSC in hopes of enabling Fireteam Osiris to reach Blue Team.

At some point prior to October 28, 2558, a Guardian activated on Samuron pulling a D79-TC Pelican to Genesis. As well, a Guardian on New Carthage awoke, fighting two Prowlers.

Aftermath
After some time, the arrivals of Guardians on Genesis slowed somewhat as various disparate forces battled one another and the Created on the world. Seemingly content with the Guardians collected, Cortana and the Created unleashed them as part of their Reclmation.

List of appearances

 * Hunt the Truth
 * Halo 5: Guardians
 * Halo: Legacy of Onyx
 * ''Halo: Point of Light