Tessagamil's population was long ruled by clans of divination, each representing their own respective view of the proper way to acquire prophecies. When the Emperor of Mankind launched his Great Crusade, people of Tessagamil already knew of this and waited their new lords humbly. Planet, and its population, took a major blow during the Horus Heresy and the planet was finally revered as a Shrine World of a sort by Ecclesiarch Veneris I and later as a Cemetery World by his successor Veneris II.