Cryptum

Cryptums, or Warrior Keeps, were objects created by the Prometheans, the highest class of Warrior-Servants in the Forerunner ecumene.

Background
A Cryptum is a sealed capsule where a high-ranking Promethean would enter self-imposed exile as punishment for failure or dishonor. They are spherical in shape, with a dark gray outer casing broken by a pattern of angular, orange-glowing "cracks." When in use, their Forerunner occupants would enter a state of meditative hibernation known as "timeless xankara". During this time, the Forerunner would become unaware of the physical world around him, and could remain in a state of suspended animation for thousands of years. Cryptums required an extraordinary amount of force to breach once sealed. They denied access to every species except Forerunners.

While the Cryptum preserved the consciousness of the Forerunner inside for an indefinite period, the Forerunner's physical body would still deteriorate, albeit at a significantly reduced rate. The body of the Forerunner would shrivel and lose most of its fluids, in a process similar to mummification. Once the Forerunner was removed from the Cryptum, the body would be placed in a restorative bath, and the body's supply of electrolytes, nutrients and other essential substances was thereby replenished. The body's muscle structure would then be regenerated, a process requiring several days.

The nature of a Cryptum was unknown to most Forerunners, including Bornstellar Makes Eternal Lasting. However, he was aware that the violation of a Cryptum invoked dire consequences, one of which was angering the powerful Prometheans.

A Cryptum was discovered in Djamonkin Crater by the young Forerunner Bornstellar Makes Eternal Lasting, containing the meditating Didact. Another Cryptum, also containing the Didact, was discovered over 100,000 years later by John-117 and the AI Cortana on the Forerunner Shield World Requiem. This Cryptum had not withered the user, as the Didact remained as physically fit as he had been when he entered; it is unknown if this was the work of the Cryptum itself or the fact that the Didact wore his personal armor during hibernation. This Cryptum was able to travel at massive speeds, yet had no weapons and was vulnerable to UNSC ones such as MACs and missiles. It also had the capability to scan its surrounding environment or data networks in order to gather information. It also appeared to be capable of traveling through slipspace if necessary. This Cryptum was destroyed when the Master Chief detonated a Havok-class nuclear warhead inside the Didact's flagship, Mantle's Approach which it had joined with.

Trivia
The millennial seal on the Didact's Cryptum placed on Earth was sealed by two forces known as "The wisdom of Harbou" and "strength of Lang". Who or what Harbou and Lang were is unknown. However, they appear to be a reference to the German actress and author Thea von Harbou and the film producer and screenwriter Fritz Lang, who were married and made several films together.

List of appearances

 * Halo: Cryptum
 * Halo: Primordium
 * Halo 4