Timeline of the Warhammer 40,000 Universe

This article relates to events in the universe prior to the late 41st Millennium in the Warhammer 40,000 setting. throughout this article, comparative references to dates will be with respect to the approximate time period 990.M41 to the end of 999.M41. This is the time period in which the perspectives of the Imperium and the Eldar are particularly relevant.

Pre-History
The Slann*needs review and references*

The Slann are an incredibly ancient race in the Galaxy, pre-dating all other known corporeal beings. The Slann are commonly thought to have been an advanced race in excess of sixty million years ago and are responsible for the creation or advancement of most of the currently active species.

The War in Heaven*likewise*

A conflict arose between the C'Tan, immensely powerful, incorporeal beings existing (almost uniquely) in the material universe, and the Slann. The Slann, being physically weak and few in number but mighty in intellect and power, created the Eldar race and stimulated the genesis of the Eldar Gods as (originally) demigodly beings who fought alongside their mortal charges. In response, the C'Tan fashioned themselves corporeal avatars known as a Necrodermis from a metal-like substance and enslaved the Necrontyr race by bonding them with armoured shells, which became known as Necrons.

Eventually, the C'Tan were forced to withdraw, hiding for many millions of years while the Necrons hibernated on forgotten 'Tomb Worlds' inside massive complexes, tended by artificial mechanoid constructs and only occasionally disturbed by the probing of younger race's explorations.