- “Now, Prophet...your end has come.”
The Battle of the Citadel was a battle between the UNSC/Separatist/Forerunner constructs Alliance, the Covenant Loyalists and the Flood. It was the last major battle to be fought in the Human-Covenant war.
Having secured the Cartographer, the majority of the remaining UNSC and Sangheili converged on a communications citadel that housed the remaining Covenant Loyalist forces and the High Prophet of Truth. The initial landing forces were transported to the various locations by five Pelicans and two Phantoms. The group split up and two Pelicans, holding Johnson and many Marines to the Third Tower. The two Phantoms landed at the Second Tower, dropping Thel 'Vadam and several Elites straight into the fighting. Two of the remaining Pelicans, including Kilo 023, headed towards the First Tower, where they met heavy fire, resulting in one of the Pelicans being shot down. Kilo 023 was carrying Spartan-117 and three ODSTs.
Battle of the First TowerEdit
John-117 and the three ODSTs proceeded up the beach, eliminating all Jiralhanae and Unggoy resistance, until they came to an Anti-Aircraft Wraith and a pack of Jiralhanae, led by a War Chieftain. John eliminated the Jiralhanae and destroyed the Anti-Aircraft Wraith. Commander Keyes then dropped off a Warthog, a Mongoose and several more Marines. John proceeded to drive inland to the tower and destroyed a Wraith, a Shade, several Ghosts and Prowlers guarding the outside of the building. Commander Keyes once again aided John-117's progress by dropping several weapons. John then destroyed another Shade and cleared out the rest of the enemy resistance outside the tower. John and the remaining Marines battled their way to an elevator that would carry John up to the shield switch, which was guarded by several Brute Minors, two Brute Bodyguards and another Chieftain. He quickly dispatched the Brutes and deactivated the shield, just as Thel 'Vadam did the same at tower two. When Johnson’s team failed to deactivate the barrier, the Commander ordered John and the Arbiter to get to the third tower.
En Route to the Third TowerEdit
Having made his way downstairs and outside, John then proceeded back to the beach. At the beach, John was ordered to take a Hornet to give support to two Phantoms and a Pelican to get to the third tower. On the way, John destroyed an AA Wraith and many Banshees. In front of the Third Tower, John used his Hornet to destroy a Loyalist Phantom. Before clearing an LZ for the Commander, John had to destroy two AA Wraiths, two Shade Turrets and several Banshees. He then used the Hornet to kill the Brutes remaining outside of the tower. The Arbiter then dropped down to help John.
The Third TowerEdit
John, Thel 'Vadam and seven Elites stormed the tower and met with a Lekgolo pair and a large swarm of Yanme'e. The group suffered several casualties and continued on after removing the resistance. They continued until they came to another elevator. John preceded up alone and fought several Brute Stalkers and yet another War Chieftain. John killed these Brutes and deactivated the barrier. At that moment, the Flood infested High Charity crashed into the Ark. Before crashing, High Charity sent out chunks of a Flood infested ship to spread the infection. One of these chunks hit the Separatist ship Shadow of Intent and causes "significant damage", rendering it useless in the rest of the battle. John fought his way though the Flood to reach the Arbiter and together they fought the Flood back and reached the rally point where the Marines were gathering. There they had a Scorpion Tank, an M12G1 LAAV Warthog and a Mongoose. The Marines and the surviving Elites then drove through the cave and onto the Citadel.
The group moved through a valley and along the cliffs, fighting the remaining Brutes, Ghosts, Prowlers and Wraiths. Having dealt with the resistance, John got into a Hornet as two Scarabs dropped from orbit and the last battle of the Human-Covenant War commenced. The UNSC and Sangheili used several Hornets, a Pelican, a Scorpion Tank and several Warthogs to fight the Scarabs and the oncoming waves of Banshees, Ghosts and Prowlers. John had soon destroyed one of the Scarabs, allowing the UNSC to concentrate their firepower on the last Scarab. When that was destroyed, the Marines were ordered to get rid of the survivors while The Arbiter and John went to deal with Truth.
En route to the top of the Citadel, Truth intercepted his broadcast to his faithful populace. It showed and disclosed Johnson being held captive by a Brute Bodyguard. When Commander Keyes asked how close John was, he replied that he wasn’t close enough to reach the captive Sergeant. Meanwhile, Johnson was antagonizing a Brute Chieftain in an attempt to kill him, so the Truth couldn't activate the rings. Commander Keyes then used a Pelican to crash through the window and rescue Johnson. Commander Keyes kills two Brutes before getting killed when Truth shoots her seven times in the back with a Spiker. Truth, with the help of a now disheartened Johnson, activates the remaining Installations. When the elevator reached the top, and John and the Arbiter got off, two Tank Forms offered their help to switch off the Installations and stop a galaxy-wide genocide. John, the Arbiter and the Flood battled their way through the remnants of the Loyalists and reached the platform where they found Johnson with the dead body of Miranda Keyes. Thel 'Vadam then executed Truth while John deactivated the Installations. When the Flood turned on them, John and the Arbiter were forced to double-back and find another way out. Fighting through the hordes of Flood, they found a chute that they dropped down and subsequently found that the Ark was building a second Installation 04.
- The UNSC/Separatist beach landing was reminiscent of the landing scene in the Halo: Combat Evolved level The Silent Cartographer.
- This battle was the only time the Flood allied with Human or Covenant forces.