150,000 BCE


 * Circa 150,000 BCE, the Forerunners are claimed by some records to have risen as the preeminent species in the Milky Way Galaxy by advancing technological discoveries gathered from the remnants left by prior ancient races. Believing themselves responsible for the lives of all those less advanced then they, the Forerunners initiate the Mantle.
 * Humanity is believed by the Forerunners to have "moved their interstellar civilization outward along the galactic arm" around this time, possibly to escape Forerunner control.