High Charity is a mobile planetoid station of the Covenant. It is a large bulb-shaped structure estimated to be 348 kilometers (216.108 miles) in diameter, which is actually a massive starship. It can be likened to the Covenant analog hundredfold to the UNSC Hopeful in terms of identity.
It is capable of Slipspace jumps, like any other Covenant capital ships. The city houses the majority of structures sacred to the Covenant, such as the Council Chamber, the Mausoleum of the Arbiter, and the Sanctum of the Hierarchs.
Appearance
The interior of High Charity is effectively a massive city. In the center of the city is a Forerunner Ship which had been modified to power the entire city and its engines. The city contains several holy locations to the Covenant, and it is the home of the High Prophets and the High Council.
High Charity's city is similar to the Unyielding Hierophant in that although it appears to be completely artificial, it contains courtyards and other "natural" seeming locations throughout the city. It also boasts a great deal of the Covenant's unique architecture.
The exterior of High Charity is similar in appearance to a mushroom. It is from the apex of this "mushroom" that the Forerunner Ship is launched from at the end of Halo 2. This is best seen on the High Charity Wallpaper.
History
Little is known of High Charity before its depictions in Halo: First Strike and Halo 2. It is known that High Charity has its own fleets, consisting of thousands of carriers, supercarriers, and cruisers. One of these fleets was the Second Fleet of Homogenous Clarity.
It seems that High Charity was in one place for an extended period of time, as they set up a network of slipspace probes by the fleet around High Charity. Nothing larger than a centimeter in diameter could drift too close, as the ships obliterated anything in range, including ships that failed for a milisecond to transmit the proper clearance codes.
In 2552 a UNSC operation was planned to locate High Charity in order to capture members of the Covenant leadership, however at the time the UNSC still believed that High Charity was a planet.
Upon the discovery of Installation 04, High Charity was supposed to perform a slipspace jump to the Halo along with its fleet, where the High Prophets would activate the ring to send the Covenant on the Great Journey. They sent the Fleet of Particular Justice to secure the ring in preparation for High Charity's arrival, but they did not know about the Flood, and did not expect interference from UNSC personnel. When High Charity and its fleet arrived at Threshold, they found that both the Halo and the Fleet of Particular Justice had been utterly destroyed.
After The First Battle of Earth, the High Prophet of Regret sent the coordinates of Installation 05 to High Charity. The planetoid and its fleet arrived just in time to watch the Master Chief kill Regret. It then held position over Installation 05 until hostilities erupted between the Brutes and Elites, as a new Civil War of the Covenant broke out.
During the chaos of the war, the Master Chief infiltrated High Charity, as did The Flood, using the UNSC In Amber Clad to ferry legions of Combat Forms to the station, and Pelican dropships to spread Carrier Forms. Within the city a vicious melee ensued among Brute forces, Elite forces, and Flood, all bent on destroying one another. The unfortunate Master Chief was caught in the middle of this, but managed to escape.
Eventually, the Forerunner ship at High Charity's core took off, with both the Prophet of Truth and Master Chief inside, leaving behind Cortana. It appears that the Covenant forces on both sides completely abandoned High Charity afterwards, and it was completely infested by the Flood, as the Flood organism known as Gravemind took complete control of the Sanctum of the Hierarchs, using the Council Chamber itself as his "throne room."
Whether it will be reinhabited or destroyed in the future (Halo 3) is unknown. However, with the Forerunner ship, its source of power gone, it is likely that whatever automated defenses the city has will not work, and with the Flood running unopposed in the city, there is a good chance it is destroyed. Of course, the Flood had shown genius with machines in the past, so they may find a new way to power the city, giving them even more of an upper hand in Halo 3.