|Map||Basic Data||Planetary Image|
Diamat is a Forge World of the Imperium. During the Horus Heresy, Warmaster Horus moved its Titan Legion, the Legio Gladius, to the galactic south to leave it vulnerable for his upcoming rebellion.
When word of the Heresy spread, the Dark Angels under Lion El'Jonson led a small force to the world to secure its powerful siege engines against traitor forces. A brief battle broke out between Dark Angels and Horus' forces and both tried to secure the world, one where the loyalists eventually prevailed.