Fortress-class vessel

Fortress-class vessels, more commonly known as fortresses or fortress ships, were massive warships used by the Forerunner military. The Fortress' name is in reference to the ship's size and power.

Design details
While not all of a single unified design, Fortress-class vessels were known to be some of the largest and most powerful vessels in the Forerunner navy. From bow to stern, some many of these ships were approximately 50 kilometers long and 10 kilometers across at the widest point. The hull was generally divided into three sections and the foremost section of the ship sometimes featured a massive hemispherical structure that was 10 kilometers in diameter. The dome's hollow core served as living space for hundreds of thousands of Forerunner Warrior-Servants. Below the dome was a mid-section composed of layered platforms supporting landing bays and weapon mounts. The aft section of the ship was a long "tail" covered in gun emplacements and other forms of energy weaponry.

As previously noted, Fortress ships did not follow a single design and could be encountered in different shapes and sizes; ships used toward the end of the Forerunner-Flood war measured up to 100 km in length with far more destructive capabilities. Extremely large examples of Fortresses (presumably such as the aforementioned hundred-kilometre example) may be fitted with heavy ion weapon systems as their primary superweapons. Fortress-class ships may also incorporate Minoris Assembler Vats into their structure to allow for the mass on-site fabrication of lower-tier constructs such as Sentinels.

Complement
Due to their behemoth structure, a single fortress ship was capable of carrying and deploying enormous amounts of harriers and weapon-ships. During battle, fortresses would first deploy thousands of swift attack craft in outward-fanning formations. They also had automated screens of weapon-ships, up to a million of which could be commanded by individual Warriors.

Ships of the line

 * Deep Reverence

Forerunner-Flood War
During the Battle of the Capital, a battle group of fortresses and cruisers attacked the original Halo installations under Mendicant Bias's control. Later, in one of the final battles of the war, the Falchion's interstellar defensive clench comprised twelve fortresses—only partially mobile due to space-time debt—for a fleet of 700,000 harriers.

Covenant
During the early years of the Covenant empire, prior to around 648-791 BCE, a derelict Fortress-class vessel was discovered in orbit around Tuluk'katho. The ship's nigh-unbreakable superstructure was used as the basis for the Spine of the Gods, the large "tail" extending through the bottom of the Covenant's capital-station High Charity. The site of this discovery became the site of High Charity's construction.

List of appearances

 * Halo: Cryptum
 * Halo: Primordium
 * Halo: Silentium