Cryptum

The Cryptum was seen in the Halo 4 E3 sneak-peek trailer. It seems to have been buried underground until the flew overhead.

The Cryptum is first encountered by the Master Chief during the campaign level Forerunner. It contains the Forerunner Didact. The Cryptum itself resides within a spherical "satellite" in the center of the hollow Shield World Requiem.

Overview
Before Master Chief and Cortana arrived on Requiem, the Cryptum served as a prison for the Didact. However, once the UNSC Infinity arrived in orbit around Requium while searching for the origin of the distress beacon of the crashed UNSC Forward Unto Dawn, the Didact used the signal from the Infinity to lure Master Chief and Cortana to the docking complex for the Cryptum. Thinking that the Cryptum was a relay, Master Chief interacted with the Cryptum's control panel in an attempt to contact Infinity but unknowingly released the locks on the Cryptum. The Cryptum then retracted its metal plates and revealed the Didact. After the Didact's first confrontation with Master Chief the Cryptum serves as his transport.

The Didact takes the Cryptum to the crash site of the Infinity and begins scanning the ship. Master Chief is eventually able to re-acivate the Infinity's defense systems and forces the Cryptum to move away. The Cryptum then retreats and moves to a docking structure where it errects a shield around itself and coordinates the Storm Covenant fleet.

Master Chief and Cortana pursue the Cryptum to the docking complex while the Infinity flees the planet. There they try to prevent the Didact from escaping. After shutting down the Cryptum's shield, Cortana attempts to move several Forerunner structures around the Cryptum in order to imprison it. However, one of Cortana's rampant personalities stops her and the Cryptum is able to escape and unite with the Didact flagship, the Mantle's Approach, which then leaves Requiem.

Trivia

 * The Cryptum is briefly seen at the very end of the "Making Halo 4: Return of the Forerunners" video. It is seen in what appears to be a dark chamber with the Cryptum sitting on what appears to be a dock for it.
 * The Cryptum is a rare example of Forerunner technology with a rounded shape. The only other examples are Monitors and the various Forerunner constructs.

Appearances

 * Halo: Cryptum
 * Halo 4