A Sept, also known as a realm, is a star system, or a series of star systems, colonised by the T'au Empire; this includes all colonised planets, moons, and holdings such as orbital stations, and void structures within the system.[10a][10b]
Each Sept is named after its Sept World, also known as Prime Planet or Capital Planet, from which the Sept is governed and is denoted by a different Sept Symbol and colour for each, often related to the unique culture of each Sept.[10b]
Tau Septs are managed by an Elemental Council. This includes representatives from the five Tau Castes (Ethereal, Fire, Air, Water, and Earth) as well as a 6th observer seat that goes to a prominent member of an Auxiliary race for an "outside perspective". However final word on the Council ultimately goes to the Ethereal representative.
- T'au, homeworld of the Tau. Capital and spiritual, political, cultural, and administrative centre of the Tau empire. Its citizens are considered especially learned and wise.
- Isla'su, homeworld of the Greet.
- Pech, homeworld of the Kroot.
- Sha'galudd, homeworld of the Nagi.
- Vespid, homeworld of the Vespid.
First Phase Expansion
The Tau homeworld and the First phase colonies are of major importance and form the hub of the empire.
- T'au'n, first offworld colony, Tau from this world are considered to be pioneers.[7a]
- D'yanoi, having been isolated for a time from the empire, its inhabitants are considered somewhat rustic and backwards.[7a]
- Bork'an, centre of learning and academia.[7a]
- Dal'yth, cosmopolitan and trader-friendly.[7a]
- Fal'shia, centre of technological development, Tau from here are considered great problem solvers.[7a]
- Vior'la, a major military centre of the empire, its Fire warriors are considered especially aggressive and skilled.[7a]
- Sa'cea, another military centre, this sept has a very high proportion of very disciplined and honourable Fire Warriors.[7a]
Second Phase Expansion
- Au'taal, a beautiful sept, whose citizens are considered easygoing and often lazy.[7b]
- N'dras was abandoned for unclear reasons. Its remaining inhabitants are regarded as untrustworthy, quick-tempered, and of brooding countenance.[7b]
- Ke'lshan has suffered several raids by several alien races. Tau from this sept have grown mistrustful, solemn, taciturn, unfriendly and sometimes openly hostile to alien races. Ke'lshan was invaded by Hive Fleet Gorgon and played an essential role in stopping it.[7b]
- Elsy'eir is known for its poetry and artwork. Its citizens are considered intellectuals and well-respected for their creativity.[7b]
- Tash'var was raided several times by Orks and pirates. Its people are regarded as tenacious, hardy, practical and courageous.[7b]
- Vash'ya seems to be primarily inhabited by members of the Air caste.[7b]
- T'olku or Tol'ku is known for the skill of its Ethereal diplomats.[7b]
Third Phase Expansion
The Third Phase Expansion was convened on 977.997.M41 on the word of Aun'va. Commander Shadowsun was placed in command, and secured at three new septs for the Tau Empire. During the Zeist Campaign of 999.M41, Space Marines forces counterattacked against the expanding Third Sphere, drawing the Third Sphere to a temporary halt. The three septs formed from the Third Sphere Expansion are:
- Ksi'm'yen's colonists seem to be associated with luck, subtlety and opportunistic subterfuge.[7c]
- Fi'rios whose pioneers are recognised for a tenacious refusal to accept defeat, tempered by a stoic acceptance of the price all must pay in the furtherance of the Greater Good.[7c]
- Mu'gulath Bay, previously known as the Imperial Hive World of Agrellan. (Destroyed)[7c]
Fifth Phase Expansions
After the ill-fated Fourth Sphere of Expansion reestablished contact with the Tau Empire after decades of being thought lost, a new campaign was immediately launched through a wormhole known as the Startide Nexus. Rapidly, worlds on the other side of the rifts have been colonized.
Known Fifth Sphere septs include:
These are Septs that are not credited to a specific phase of expansion; some have been formed individually, through opportunity or a smaller-scale invasion. Some may not even be Septs, but rather a splinter of another Sept.
- Dy'aketh — formerly the Imperial world of Drachenvol[7f]
- Queh-quih[17a], a "Kroot Sept"
Besides the populous septs, there are also sparsely populated colonies. Only a few names are known. Locations of unstated status are put here as well.
- Atari Vo[18b]
- Cano'var[18b] — Lost during the Second Sphere of Expansion to "robotic creatures" with "strange energy weapons"
- Es'Tau[4a], settled during the Second Expansion.
- Fal'skio[9b] — A research world, site of Drukhari attack
- Gates of Petros[9c] — Site of Drukhari attack
- Ho'sarn — was evacuated in 902.M41 as Hive Fleet Gorgon approached. But the evacuation fleet was ambushed by the Hive Fleet and completely slaughtered.
- Ka'mais — invaded by Hive Fleet Gorgon in 902.M41. A hidden Necron fleet emerged from Ka'kais' dead moon and destroyed the outnumbered Tyranid ships, but then continued to land on Ka'mais and harvest the planet.
- Kor'var[18b] — Site of the destructive ongoing Kor'var Campaign
- Ky'san[7d] — Site of a Kroot uprising
- Sha'draig — invaded by Hive Fleet Gorgon in 900.M41. Gorgon was eventually driven off the world, but not before it was almost completely consumed by Ripper swarms.
- Shans'et — formerly the Imperial world of Gossamehr
- Shi'yen[7g] — Colony for client races
- T'ros, settled during the Third Expansion, currently being contested by the Imperium.
- Va'yun[18b] — Raided by Eldar Corsairs
- Vas'talos, previously known as the Imperial Fortress World of Prefectia.
- Xynd[9a] — Home to the "airborne Floating Canopies of Xynd", site of Drukhari attack
During the First phase expansion, the homeworlds and colonies of the Kroot and the Vespid were also incorporated into the Tau empire. Notice that these star systems are not considered septs. In addition, there are an unknown number of former Imperial worlds in the Tau Empire, such as T'ros. Some or all of which might still have a Human population.
- Pech, homeworld of the Kroot. According to the maps, there are eight star systems inhabited by the Kroot (including Pech). We know the name of only one, Krath, where the Tau first encountered the Kroot.
- Caroch, Kroot world
- Akchan-Kur, Kroot world
- Vespid, homeworld of the Vespid.
- Isla'su, homeworld of the Greet
- Sha'galudd, homeworld of the Nagi
- Roksh XVI — site of a secret Tau listening post, the planet was part of the Roksh system that was home to the Rokshashi Wealthweb merchant guild before the entire system was consumed by Hive Fleet Gorgon in 689902.M41.
- Yuun'chen, Kroot world
Three Artefact worlds are located within the borders of the Tau empire. As the name indicates, ancient artefacts of unknown origin have been discovered there. It is not known if these worlds have Tau colonies at all.
- Arthas Moloch, a dead world where Commander Farsight found the Dawn Blade.
- Landfall - Discovery of an ancient Syrshin star chart here led to a means to travel from this planet to what would become Sept Velk'Han in the Jericho Reach.[13b]
- 1: Codex: Tau Empire (4th Edition), pg. 42
- 2: Warhammer 40,000 5th Edition Rulebook, pg. 129
- 3: Codex: Space Marines (5th Edition), pg. 48
- 4: Kill Team (Novel) by Gavin Thorpe:
- 5: Imperial Armour Volume Three - The Taros Campaign, pgs. 130-146
- 6: Codex: Tyranids (5th Edition), pgs. 18–21
- 7: Codex: Tau Empire (8th Edition):
- 8: Voice of Experience (Short Story)
- 9: Codex: Drukhari (9th Edition):
- 10: Codex: Tau Empire (6th Edition):
- 11: Codex: Tau Empire (9th Edition), pgs. 8-9
- 12: Aeronautica Imperialis: Taros Air War, pgs. 34-35
- 13: Deathwatch: The Achilus Assault:
- 14: White Dwarf July 2017 — Battle Report: Da Tale of Badrukk's Loot
- 15: Codex: Imperial Knights (8th Edition), pg. 54 — A Tapestry of Glories: Daemonic Vengeance
- 16: War Zone Damocles: Kauyon pgs. 95–101
- 17: Fire Warrior (Novel):
- 18: Codex: Tau Empire (7th Edition):
- 19: White Dwarf January 2017, pg. 111
- 20: Codex: Necrons (7th Edition), pg. 83
- 21: War Zone Damocles: Kauyon, pg. 99
- 22: Shadowsun: The Patient Hunter (Novel) - Chapter 1