Sentinel wall



Sentinel Walls are massive walls on Halo installations intended to serve as means of containment if primary measures fail in the event of a severe Flood outbreak. As their name suggests, the walls house numerous Sentinels to both repair the facility and keep the Flood from spreading beyond the wall. A Sentinel wall surrounded the Quarantine Zone around the Library of Installation 05 to keep the Flood from spreading.

Background
The wall appears to have been designed to keep the outbreak of Flood around Delta Halo's Library contained within the Quarantine Zone. It is honeycombed with tunnels for the Sentinels to travel through. Sentinels and Enforcers keep the Flood contained, while Constructors keep repairing the damage that the Flood inflict on the wall. In addition to the massive physical wall, the Sentinel Wall also projected an energy barrier known as a Containment Shield.

Battle of Installation 05
Despite the efforts of the robotic keepers, the Flood were released when the Arbiter penetrated the defenses and deactivated the containment shield around the wall. During the battle on Installation 05 the Arbiter was sent into the wall to deactivate the shields keeping the Flood in the Quarantine Zone in order to let other Covenant forces fly over the wall towards the Library.

Installation 00
Installation 00 contained a similar, though far smaller, security wall structure near its Cartographer. Inside the wall was a deep chasm and an energy bridge allowing passage over it. A terminal was located within the wall near the activation switch for the energy bridge.

When the UNSC forces landed on the Ark during the Battle of Installation 00, they were to secure a landing zone for the to land. The ground teams pushed through Covenant loyalist forces but were prevented access to the Cartographer by the wall. After the Forward Unto Dawn landed nearby and deployed a convoy of multiple vehicles, Commander Keyes suggested they go through the wall. The UNSC forces returned to the wall and with the assistance of 343 Guilty Spark, successfully passed through.

Trivia

 * A section of the Sentinel Wall is clearly visible on the Halo 2 campaign levels Delta Halo and Regret, as well as the multiplayer map Containment. The Sentinel Wall can be visible and seen beyond the Prophet of Regret's Forerunner temple on the level Regret, denoting its massive structure and size.
 * It is unknown whether the other Installations have this feature, as the player would have bypassed the wall due to the Monitor's use of the teleportation grid on Installation 04.