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The Forerunner caste system was a system used to rank Forerunners in society. Castes were divided into several tiers, including forms, rates, and Maniples.

Practices
Adolescent Forerunners, known as Manipulars, were not associated with any particular caste. However, upon maturing, each individual Forerunner would be assigned to a caste, mostly in accordance with the caste of their parents. For example, Bornstellar Makes Eternal Lasting was expected to become a Builder like his father.

Each caste had their own ceremonial headgear, worn only on special occasions. However, on a certain day in the Grand Star Season, every Forerunner wore the same style.

Builders
The Builders were responsible for the construction of a majority of Forerunner architecture. As such, they were most likely responsible for creating the Halo Array and Onyx. The father of Bornstellar Makes Eternal Lasting was a Builder.

Miners
The Miners were the caste responsible for obtaining the materials required for the work of the Builders.

Lifeworkers
The Lifeworkers specialized in biology and medicine, especially with the experimentation of various forms of life. It was not uncommon for Lifeworkers to receive their own planets for experimentation. The Librarian was a Lifeworker.

Warriors
The Warriors were the primary military caste in Forerunner society. They were most likely responsible for piloting space vessels as well as fight on the ground. The Didact was most likely a Warrior.

Warrior-Servants
Warrior-Servants were another caste, separate from the Warriors. They were responsible for, among other things, piloting War Sphinxes during the Human-Forerunner War. The use of the word "servant" in their name likely implies that they were of lower social status than Warriors. The Prometheans were an elite group of Warrior-Servants.

List of appearances

 * Halo: Cryptum