The Ark (level)
From Halopedia, the Halo wiki
Summary
The Ark is a mysterious Forerunner device from which all the Halos can be activated. In the end of Halo 2, Delta Halo is armed and then unexpectedly shut down, causing it to send a superluminal signal to all other Halos in the galaxy, putting them on standby mode. 343 Guilty Spark informs Miranda Keyes and Sergeant Johnson that the Halos must now be activated from "The Ark". The location of the Ark is speculated as being on Earth, buried under the African soil near New Mombasa. It has been proposed that the effect of the ship commanded by the Prophet of Regret jumping into slipspace inside the Earth's atmosphere had a devasating effect on everything around it. This caused the destruction of New Mombasa, and aided in unearthing "The Ark". Whether this effect was intentional or coincidental is all specualtive at this point.
In the Halo Graphic Novel, Second Sunrise Over New Mombasa, a transmission is intercepted between the Covenant assualt forces stating that once the humans have been dealt with, they would start uncovering the Ark, offering further proof that the Ark is most likely on Earth and located under the New Mombasa area.
It is expected that Halo 3 will reveal more details about the Ark. The Halo 3 Announcement Trailer depicts the Ark firing a beam of white energy straight into the sky, through the center of swirling clouds. This structure can be confirmed to be the Ark from a concept sketch found in the DVD (seen right). The structure in the Halo 3 Announcement Trailer has not officially been announced as the Ark by Bungie however.
It is also believed, though this is purely speculative, that the Ark may have sheltered the Forerunners after Halo's first use, which then evolved into humanity. In the Bible, God floods the Earth to cleanse it of all life, which has grown evil and wicked. However, he saves a group of righteous humans and two of of all animals by telling them to build and seek refuge in a ship, called the Ark. Thus it is a possibility that in Halo, the Ark is a structure or device that shields those using it from the effects of the rings' activation. The humans on Earth might have descended from those who were protected by the Ark during the first activation of the rings.
Further evidence to suggest that the Forerunner and human race are one and the same manifests itself in one of the final cutscenes of Halo: Combat Evolved. Guilty Spark, upon scanning the files of human history aboard the severely damaged Pillar of Autumn, remarks on, "Our lost time." This subtle distinction, coupled with the knowledge that guilty spark refers to Master Chief and Miranda Keyes as the "Reclaimer" and acts as if they have met before, allows one to reasonably conclude that the human race is all that remains of the Forerunner. It's incredibly ironic, especially when one considers how the Covenant have essentially worshipped Forerunner technology and, at the same time, are driven by their dogmatic beliefs to eradicate the human race.
Trivia
The name of the Ark may refer to the biblical story of Noah's Ark that was built to save Noah's family and a number of animals from a massive flood, "the ark saves humanity from the flood." However, it's possible that it has a double meaning referencing to the Ark of the Covenant.