Barrier tower

. A Barrier Tower is a Forerunner shield-generation tower.

At least three of them surrounded the Citadel on Installation 00, projecting an energy shield that denied access to the Citadel. They could be individually deactivated by means of a holographic control panel on their upper floors. Multiple Barrier Towers also surrounded Installation 05's Quarantine Zone, most likely mounted on top of the Sentinel Wall.

Battle of Installation 00
During the battle of Installation 00 in late 2552 between the United Nations Space Command/Covenant Separatists alliance and the Covenant Loyalists, the UNSC and the Elites sought access to the Citadel, but were barred by means of the energy shield of the three Barrier Towers. Commander Miranda Keyes coordinated a simultaneous assault on all three towers, ordering SPARTAN-117 and a small Orbital Drop Shock Trooper and Marine force to take the first east most Barrier Tower, the Arbiter and the Elites to take the middle Barrier Tower, and for Avery J. Johnson and a Marine detachment to assault the west most Barrier Tower.

Each tower was heavily protected. The tower which SPARTAN-117 was assigned to take out was protected by an Anti-Aircraft Wraith as well as multiple Shade turrets and a Chieftain guarding the controls. Johnson's tower was protected by two Anti-Aircraft Wraiths, one normal Wraith, a pair of Hunters and a swarm of Drones. The controls were protected by Brute Stalkers and an armor Chieftain.

While SPARTAN-117's group and the Arbiter's group managed to deactivate their two assigned Barrier Towers, Johnson's force ran into heavy Loyalist resistance at the third tower, and Johnson's men were killed while Johnson was taken prisoner by the Brutes and taken to the Citadel itself. SPARTAN-117 was ordered to take a Hornet VTOL to attack and land on the third Barrier Tower, deactivate it and attempt to find Johnson. Even though SPARTAN-117 successfully deactivated the last Barrier Tower, he was unable to find Johnson. Immediately after the third tower's deactivation, the Flood infested High Charity appeared and crashed on the Ark's surface nearby. As it went down, it released large chunks of debris, one of which smashed through the window of the tower's control room. The chunk was actually used as a makeshift vehicle by numerous Combat Forms and Infection Forms to reach the tower and it's exterior.

Afterwards, the shield around the Citadel was lowered and the UNSC Marine Corps launched an all-out assault on the Brute-held Citadel.

Trivia

 * The "Thunderstorm" skull on Halo 3 can be found on an exterior balcony on the middle Barrier Tower where the Arbiter and his Elites went in the start of the level, "The Covenant".
 * Using a glitch to get to the ringed structure in which the barrier is projected, one can simply pass through it unharmed and without resistance. Obviously, this is only the case because Bungie didn't expect anyone to be able to reach the barrier.
 * All three of the Forerunner Terminals found on this level lie within Barrier Towers.

Related Articles

 * Forerunners
 * Installation 00