The empire of the Forerunner was indeed vast. Beneath the surfaces of countless worlds their artifacts and installations lie buried, for the most part untouched by the passage of time. Stones and relics found at each location contained coordinates leading to even others. Many of the Human worlds were accidentally located by the Covenant this way: Reach and Earth, being the most recent examples. They were also used to find Halo 04, and from some relic on Earth (though he apparently had not discovered the "main facility" yet) Regret located Halo 05. The Halos, the seven rings, left in their perpetual orbits after activation and the subsequent destruction of their creators, are nothing short of astounding. But as revealed by 343 Guilty Spark, there remains yet another piece of their puzzle.
Hypothesized and speculated on for some time but only revealed in Halo 2's conclusion, the Ark is still shrouded in mystery. Located on Earth (though it was once theorized to be on the moon; both the possible "2001" homage and talk of a moon-based, low-gravity level contributed to this), the Ark is a primary center from which the entire Halo network may be remotely activated. It is not known whether the Ark will preserve the lives of those who set it off (unlike the Halos which destroy even the life upon their surfaces), but because the name itself is an allusion to a biblical sanctuary during a storm, it is implied that it will.
Does the location of the Ark have anything to do with the Prophets' mad zeal to annihilate Mankind? What does it mean that Humanity occupies the world of the Ark, and possibly the last haven of the Forerunner in this galaxy? Is this yet another clue as to why 343 seems content to call every Human a "Reclaimer", yet not a Forerunner? Stay tuned...
Une histoire complete sur l'Arche