The exact date of founding of the Tau empire is unclear, however the reasons behind its foundation are. In [[Tau]] prehistory, they lived in tribes on the desert plains, hunting and gathering their food. As their race aged, they expanded to all environments of [[T'au]], adapting to each new environment. The Tau of the plains became strong and skilful hunters, larger and stronger than most other Tau. The Tau of the mountains developed the ability to soar high above the baking deserts on thermals. The Tau of the river valleys developed agriculture and metallurgy, forming the first true settlements. The development of settlements led to the need of trade, and wandering Tau began to negotiate and mediate between the disparate tribes. During the [[M35|35th Millennium]], an [[Adeptus Mechanicus]] [[Explorator]] fleet [[Land's Vision]], had discovered the Tau homeworld and determined that its population were a primitive people at the Stone Age level of development who had only just mastered the use of primitive weapons and fire.

Growing pains, caused by their For some unknown reason Tau technological advancement preceded at unusually rapid technological development led to the invention of sophisticated weaponryrate then would be expected for a newly emergent race. The Tau of the river valleys developed stone the first fortresses and crude blackpowder weapons to ward off the aggressive Tau of the plains. During this time inter-tribal conflict escalated. These fledgeling skirmishes led to the darkest period in Tau history, the Mont'auduring the end of the [[M37|37th Millennium]]. The numerous wars that broke out lasted for years. Each year thousands died as , squalid conditions and lack of access to fresh food and water created a plague that killed more Tau than were dying in the wars. The Tau were on the verge of wiping themselves out.

During this time, the Tau legends tell of the first appearance of Ethereals at [[Fio'taun]]. The Tau builder fortress city of Fio'taun was under assault siege by the an alliance of warriors from the plainsand air Tau. Though negotiation had been attempted, the fierce plain warriors would settle for nothing less than the annihilation of Fio'taun. For five long years the inhabitants held off the savage assaults with their thick walls and plentiful cannon. However, disease and starvation began to take their toll. As the tide of the siege turned, two mysterious Tau appeared. One made his way into the camp of the plain Tau, exuding a quiet authority that no Tau was able to resist. Soon, the leader of the plain warriors was persuaded to parley with the Tau of Fio'taun. Similarly, the other mysterious Tau made his way deep into the fortress. Within a few short hours, the gates stood wide open, and the Tau stood ready to talk.

The Ethereals spoke of the importance of peace and understanding between all Tau. They described a Greater Good that each Tau must strive towards. The besiegers and the besieged quickly agreed with the Ethereals and a truce was reached. Across the landT'au, Ethereals emerged, each with the same quiet authority and message of harmony and cooperation. With the Tau united, a great civilisation beganthe Tau empire was founded.

Over the next thousand years the Tau empire experienced an unprecedented period of scientific discovery and philosophical advancement. The Tau empire soon expanded continued to expand its border at a fast rate through a series of Expansion Phases. The Tau empire has gone through 3 phases of expansion already. These phases are a period of several Tau military campaigns during which nearby worlds are colonised, conquered, or sometimes peacefully persuaded to join the [[Greater Good]]. Therefore, apart from the star systems of the Tau, which are called [[Tau Sept|Septs]], the Tau Empire also includes the incorporated worlds and star systems belonging to the [[Kroot]], [[Vespid]], and the [[Nicassar]]. It is currently unknown if the [[Demiurg]] are full members, allies, or mere trading partners. The empire is composed by over twenty fully developed septs and around one hundered settled worlds, but the exact number and most of their names are unknown to us.

*¹ Aun'va's declaration of the Third Sphere from [[Codex: Tau Empire (4th Edition)]], p.42. The date of the Third Sphere's inception is drawn from multiple sources: ''5th Edition Rulebook'', 129; ''Codex: Space Marines (5th Edition)'', 48; ''Planetstrike'', 57.

**^7a: pg. 107**^7b: pg.109-111*⁸: [[Kill Team (Novel)|Kill Team]] by [[Gav Thorpe]]*⁹: [[Warhammer 40,000 3rd Edition Rulebook]] pg. 116*¹⁰: [[Deathwatch: The Achilus Assault]], pg 130*¹¹: [[Apocalypse]] p.157*{{Endn|12}}: [[Warhammer 40,000 6th Edition Rulebook]] pg.213