Each Titan is a city-sized machine. The first Titan, Anicetus, was used to help the surviving humans escape Earth and colonize Acheron after the events of Conqueror. Later, the colonists on Acheron built more Titans to terraform and create supercities on Empyrean. At the core of each Empyrean city is a Titan. All of the Titans have gone quiet since the Siege of Anicetus. The inhabitants of Empyrean now worship the Titans as gods.