Installation 00

Summary
The Ark is an enigmatic Forerunner device from which all the Halo Installations across the galaxy can be activated. In the end of Halo 2, during the final cutscene, Delta Halo is armed by Tartarus, but is then unexpectedly shut down by Miranda Keyes, causing it to send a communication, hypothesized to be constituted by tachyons, super-relativistic particles, to all other Halos in the galaxy, putting them on standby mode, primed to fire. 343 Guilty Spark informed Miranda Keyes, Sergeant Johnson and the Arbiter that the Halos must now be activated from the "Ark".

Ark on Earth?
The exact location and characteristics of the Ark have not been released by Bungie but in the wake of the Halo 3 trailer all evidence points to the Ark being the large artifact under New Mombasa:


 * In Halo 2 the Covenant ship carrying the Prophet of Regret jumped into Slipspace, for unknown reasons, just a few hundred meters above New Mombasa. This caused the destruction of New Mombasa, and unearthed a huge Forerunner artifact seen in the Halo 3 trailer.  The Halo 3 Announcement Trailer depicts a huge structure firing a beam of white energy straight into the sky, through the center of swirling clouds.
 * In the end of Halo 2, the conjecturally-named "Forerunner Ship", carrying the Prophet of Truth, jumped into Slipspace from near High Charity and Delta Halo, and for unknown reasons, voyaged to Earth, possibly towards New Mombasa, as the Forerunner Ship was headed towards Cairo Station, which is in geosynchronous orbit over New Mombasa.
 * Within the Halo Graphic Novel, in the short comic Second Sunrise Over New Mombasa, a transmission is intercepted between the Covenant assault forces stating that once the humans were dealt with in the Second Battle of Earth, they would start uncovering the Ark.
 * In the real world, a concept sketch found in the Behind the Scenes DVD (seen right) names the artifact as the ark--more specifically, it names it as "Earth_Ark", which could suggest that the Ark is, indeed, on Earth, or alternately, could be a joke by Bungie.
 * In the Cradle of Life comic, the human N'chala is residing in Africa, and the "Aliens" are building machines.
 * There is also, of course, the strongly supported theory that human life originated in East Africa, usually said as the Great Rift Valley. New Mombasa is in this area, so the Ark, supposedly, also is.

Again while the above evidence points to the structure in the Halo 3 Announcement Trailer being "The Ark", it has not officially been announced as such by Bungie.



Trivia

 * In the biblical story of Noah's Ark that was built to save Noah's family and a number of animals from a massive flood. This runs parallel to the Halo Universe story line where the Forerunner use the ark to save their species from the Flood.  Also, in yet another reference to the number seven in Halo, the Noah's Ark story is in Genesis chapter 7|seven.
 * The real world Ark of the Covenant which according to the old Testament contains the stone tablets of the ten commandments, is the holiest object of the Jewish faith. The Ark of the Covenant is popularly believed to rest somewhere in east Africa, albeit in Ethiopia rather than Kenya.
 * The "Ark" seen in the announcement trailer is structurally identical to the Forerunner sanctuary described in the final chapters of Ghosts of Onyx (albeit on a much grander scale), complete with thirteen metal fins and a brilliant, blue-white portal in the ground. However, it is shown without the thirteen concentric rings rising around the portal, which means that it was either built without them or they will raise as the Ark opens. The ark could be another safe haven from the effects of the halos like the shield world. Also the ark could contain at least one Forerunner or pictures of them.
 * In Halo 3 a rumor has been going around. That once John-117 enters the Ark he sees a hologram of the Forerunners before they were wiped out. Or where the remains of their civilization is. So that may be how we find the truth of the Forerunners.

Links

 * Halo.Bungie.Org's Ark forum.