Portal under the Mountain

The Portal under the Mountain, as it is known to the Banished, is a Forerunner slipspace portal generator facility within a larger complex buried deep beneath Menachite Mountain on Reach. It is capable of opening a portal to Installation 00.

History
Following the Fall of Reach in 2552, the Covenant Hierarchs had tasked Tartarus with discovering the "Portal under the Mountain," as they called it. After the destruction of the Holy Light—a slipspace flake taken by Spartan-II Blue Team from the Forerunner structure beneath Menachite Mountain—during the battle at Eridanus Secundus, Tartarus sent eight squadrons to comb the area for any remains. Three shards of the slipspace flake were found and presented to the Prophet of Truth on High Charity. When Truth left High Charity, he brought the shards aboard the Forerunner Dreadnought. Since the portal on Earth was found first, the need to search Reach for a portal that would take Truth to the Ark was eliminated.

In 2559, War Chief Escharum received a message from Atriox, still embroiled in a conflict on the Ark, informing him of the existence of the Portal under the Mountain as well as his plan to return to the galaxy. Atriox ordered Escharum to find the portal and activate it in preparation of his arrival. Escharum, in turn, sent the Keepers of the One Freedom, the Legion of the Corpse-Moon, and the Ravaged Tusks—all factions that had recently joined the Banished—to search for the portal and report back to him when they have found it.

By following Blue Team to CASTLE Base, Castor, a Dokab of the Keepers, discovered the location of the portal, as the human military facility sought by the Spartans had been built atop the Forerunner facility. Escharum joined the Keepers in the activation of the portal. Using the three shards of slipspace flake which had been recovered from the Forerunner Dreadnought on the Ark, Atriox passed through the portal and returned to the galaxy. Castor and his Keepers then defected from the Banished, taking Atriox's Lich through the portal to the Ark, where they intended to light the rings and begin the Great Journey. Soon after they passed through the portal, it collapsed inward on itself.

Trivia

 * High Noon, the remake of Hang 'Em High for Halo: Combat Evolved Anniversary, is set within the portal facility, as confirmed in a post by Jeff Easterling.

List of appearances

 * Halo Reach
 * Halo: Shadows of Reach
 * Sacrifice