A Gehemahnet is a massive spire capable of channeling Warp energy that is built by the Chaos Space Marines of the Word Bearers Traitor Legion on newly conquered worlds, as well as on their homeworld of Sicarus, a Daemon World located deep in the Eye of Terror. A Gehemahnet's purpose is to channel Warp energy to the world it is located on in order to transform it into a Daemon World. The material for every Gehemahnet is gathered from the rubble of buildings destroyed during the initial invasion of the world by the Word Bearers. The substance that bonds all the blocks is the "blood mortar" made from the bodies of the dead inhabitants of the unfortunate world. The creation of a Gehemahnet is a monumental undertaking, and the majority of the labour is done by millions of slaves under the direction of cruel overseers drawn from the Traitor Legion. If a slave dies from fatigue or exhaustion their bodies are simply added to the blood mortar mixture. Manufactora and hellish forges are built in close proximity to the vile edifice, providing raw material for the construction of the tower as well as the creation of Daemon Engines -- spider-like cranes created for the sole purpose of assisting in the construction of the tower.
Gehemahnets work like a magnet for daemons of the Warp that are trying to break through the dimensional barrier between the Warp and realspace so that they can infest the newly conquered world. The barrier between the Realm of Chaos and the material plane are thin in the proximity of the Gehemahnet. Daemonic entities strain from beyond to cross the thin walls and enter the physical world. When the tower is finally completed the barriers are stripped away like flesh from bone and the daemons are able to take corporeal form and transform the doomed world into the latest incarnation of a Chaotic hell.
- Dark Apostle (Novel) by Anthony Reynolds