The Eastern Fringe is an area of the Ultima Segmentum, on the very "eastern" galactic edge of the Imperium of Man. The Tau Empire originated in this area. The Eastern Fringe is also the home of the Realm of Ultramar that is ruled by the Ultramarines Chapter of Space Marines. The Eastern Fringe is so far from the heart of the Imperium that the psychic beacon of the Astronomican does not reach across its entire length. The region remains largely unexplored by the Imperium and other than Ultramar contains widely dispersed and isolated human colony worlds. It may be home to a variety of xenos species other than those that are a part of the Tau Empire, though these races also remain largely unknown to the Imperium. Of the human worlds known to exist in the Eastern Fringe, many are barbarous and uncivilised though a few maintain the standard level of Imperial technology.
- 789.M35 First Contact with the Tau - The homeworld of the Tau race, T'au, is discovered and catalogued by the Adeptus Mechanicus Explorator starship Land's Vision. An unusually violent Warp Storm in the region renders any return to the world for Imperial military forces impossible.
- 742.M41 Damocles Gulf Crusade - The Tau are rediscovered by the Imperium when they begin to expand into Imperial space and the Imperium of Man unleashes the Damocles Gulf Crusade upon the Tau Empire. The Imperial forces are forced to withdraw when Hive Fleet Behemoth assaults the Eastern Fringe.
- 745.M41 First Tyrannic War - The Tyranid Hive Fleet Behemoth begins the first Tyrannic invasion of the galaxy with an assault upon Ultramar; the Tyranids are defeated at the Battle of Macragge.
- 992.M41 Second Tyrannic War - The Tyranid Hive Fleet Kraken begins its invasion of the galaxy in the Eastern Fringe, only to be defeated by Imperial forces led by the Ultramarines at the Battle of Ichar IV and by the forces of the Eldar Craftworld Iyanden.
- Codex Imperialis (1st Edition)
- Codex: Tau (3rd Edition)
- Codex: Tyranids (4th Edition)