Diamat

Diamat is an Ultima armoury world depicted in Mike Lee’s novel Fallen Angels as a strategic objective during the Horus Heresy. This entry concerns the forge world as it appears in that account, and not any other hive settlement bearing the same name.

Horus sent Luther’s Dark Angels to seize Diamat so that its siege engines would not reach the loyalists on Isstvan. Zahariel and the Calibanite host took the stockpile of ordinatus, while the Lion’s other campaign proceeded elsewhere. Horus wanted the weapons, and the operation served his purposes. The First Legion found that the Warmaster’s favour could conceal an ambush.

Diamat remains a named instance of logistical injury to the Dark Angels during the Heresy. It is distinct from Mars, and from later forge worlds that carry no Heresy-era history. Fan summaries retain its Ultima parent and do not classify it under Caliban, under Isstvan, or as a Mechanicus shrine of the forty-first millennium.