Thanatos

Thanatos is an Oruscar tomb world that houses the Celestial Orrery, a device that maps stars and can damage them. The world takes its significance from this instrument, which is the object of the conflicts fought over it.

The Word Bearers attempted to seize the Orrery and failed. The Kardenath Dynasty then turned on its Oruscar hosts, and the siege of Thanatos developed into a civil war among the Necrons.

The Celestial Orrery gives Thanatos its standing, as a device able to chart stars and to harm them. The fighting there is also notable as a case in which an assault by an outside force gave way to open warfare between Necron dynasties.