Labyrinth Array

thumb|The Mopadan Tablet was long thought to depict the location of six of the seven Halo's. As it turns out, that which it depicts is even older, and more mysterious.In the final decades of the Flood-Forerunner War, the Forerunners placed all their hopes upon the success of the Halo Array. Few expected to survive the suicidal effort to save the universe from the menace the Flood posed, but they were determined to ensure that others did, transporting billions of species to sanctuaries safe from the Halo Effect - the millions of Shield Worlds they build, the Ark, and so on. They had intended to follow, perhaps helping the sentient creatures to reestablish themselves, and learn from their mistakes - unfortunately, the betrayal of Mendicant Bias, their greatest AI creation, proved their undoing, forcing them to activate the Array early, dooming themselves but saving all else. In the centuries that followed, the Constructs they left behind did the work their makers had intended to do themselves, returning the survivors to their homeworlds, and helping them re-aclimatize themselves.

Of course, that was the official plan. What the Forerunners did not take into account was the earlier attempts by The Architect, an early Flood researcher who had advocated a campaign of total obliteration early on.