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Fire Warriors of the Tau Empire fighting against Space Marines during the Damocles Gulf Crusade, marking the end of the Second Sphere Expansion

The Second Sphere Expansion marked the second dynamic period of expansion for the Tau Empire, when the Tau pushed further into space and established over a dozen new colonial Septs from 018.M39-742.M41. During this time, a legend arose from the Fire Caste, the greatest Tau military thinker and strategist of his age, and perhaps of any other -- Commander Puretide.

Towards the end of this period of expansion, the Tau Empire was brought into conflict with the Imperium of Man, who launched an Imperial Crusade known as the Damocles Gulf Crusade to reclaim their long-neglected territory in the Eastern Fringe region of the Damocles Gulf. The conclusion of this bloody campaign marked the end of the Second Sphere Expansion.


Following their initial success with the First Sphere Expansion and their alliance with the formidable Kroot, the Fire Caste armies of the Tau Empire were swollen by billions of additional warriors to aid the fight for the Greater Good, albeit in a more mercenary fashion than was considered ideal. With engineering centres in every Sept working diligently, the Earth Caste provided innumerable innovations, but the invention demanded by the Ethereals -- faster propulsion-technology to drive starcraft -- eluded them. At last, the quantum leap came from Fal'shia Sept, where they finalised development of the ZFR Horizon Accelerator Engine. An ingenious design, this powerful new mechanism allowed Tau voidships to attain near-light speed. It was this device that would usher in the next phase of progress. With a faster fleet and armies buoyed by an influx of Kroot Carnivores, the Tau Ethereal Supreme, Aun'Wei, declared the massive build-up for the next round of interstellar exploration and settlement to be complete. With a single command that was heard throughout the Empire, the Tau launched the Second Sphere Expansion. Branching outwards from each of the hub centres of the First Sphere colonies, great Tau fleets speared into the dark, spreading the Greater Good to worlds that from distant T'au were mere specks of flickering light.

The Second Sphere Expansion was to prove even more dynamic than the first, pushing further into space and establishing over a dozen new Septs. During this time, a legend arose from the Fire Caste, the greatest military thinker and strategist of his age, and perhaps of any other -- Commander Puretide. He led his warriors to swift victories, and star systems fell before his campaigns of conquest. Many of the Second Sphere Septs, such as Elsy'eir and Tash'var, owe their existence to Puretide's brilliant strategies, and it was his masterful counterattacks that warded off the Ork invasion that threatened to overrun Au'taal Sept. It was said that even the Orks grew to fear facing an army led by Puretide, for while the Greenskins loved to fight, the master tactician took much of the joy from their battles with his evasive, yet hard-hitting tactics. Puretide's application of strategy and military theory were thoroughly recorded and are still taught at every Fire Caste academy today.

Stellar Map of the Damocles Gulf

The last breakthrough of the Second Sphere Expansion was the successful crossing of the Damocles Gulf, a mysterious region to the galactic east that had long thwarted all attempts by the Tau to pass through. Once on the other side of that roiling and unnavigable space phenomenon, the Tau swiftly established many colonies and outposts, soon making their first contact with the single largest power in the galaxy, the Imperium of Man. After a long and subtle campaign, the Tau Empire had peaceably encroached upon many planets within the area of space known to the humans as the Timbra Sub-sector of Segmentum Ultima. The bitter and destructive wars that were soon unleashed there were unlike anything the Tau had ever experienced, and that bloody fighting marked the beginning of the end of the Second Sphere Expansion.

Contact with the Imperium

Stellar cartographic map showing the worlds of the Damocles Gulf

Since first entering space, the Tau had experienced success after success. Guided by their Ethereals, each caste had overcome every obstacle yet encountered, and none could doubt Tau ascendancy. On the far side of the Damocles Gulf, however, the Tau faced an enemy unlike any other, and the epic clashes that followed heralded the beginning of an entire new age of battle. The Tau Empire's first introduction to Humanity came not with the ruling Imperium, but with dissident elements that were operating on the fringe of that mighty dominion. The Imperium of Man is the largest realm in the galaxy, although much within its sprawling borders has never been explored or has been forgotten over its long history. The region of space around the Damocles Gulf is just such an area, a stellar wilderness where the Tau Empire had found room to take root. The Tau first encountered Free Captains, pirates and lost human colonies that had regressed so that they had long forgotten their origins and any connection to their distant birth world. Those initial contacts ranged from friendly trade negotiations to instant hostility. It was some time before the Water Caste came to grasp the fact that the humans they encountered were merely the lost remnants or willing outcasts of an incomprehensibly large galactic empire.

Worlds claimed by dissident humans were soon annexed into the Tau Empire, but there was much debate about how to approach those planets still bound to the Imperium. In typical fashion, the high-ranking caste leaders debated the situation before the Ethereals. To some of the High Council, the Imperium seemed so powerful that some aggression might lead to a war that they could not win. The leaders of the Fire Caste, on the other hand, called for war, but it was Aun'Va, an Ethereal second in authority only to Ethereal Supreme Aun'Wei, who determined the plan. The Water Caste were to integrate themselves into human worlds loyal to the Imperium, insinuating themselves into the courts of Planetary Governors. Eventually, a score of worlds within the Imperium were trading with the Tau, even in preference to each other. Alien goods, and especially coveted Earth Caste technology, flowed through these markets in blatant contravention of Imperial law forbidding trade with xenos. The time soon came to initiate the second phase of Aun'Va's instructions. Upon those Imperial worlds that were deemed ripe, Water Caste envoys whispered well-rehearsed words into willing ears. The seeds of rebellion had been long cultivated, and now bore fruit as, one by one the Planetary Governors declared themselves and their worlds free of the shackles of the Imperium's brutal rule. It had taken decades to achieve, but the Tau spread more rapidly and with fewer losses through subterfuge and diplomacy than even the most brilliant military campaign could have achieved.

Damocles Gulf Crusade

The forces of the Tau Empire fighting against the Scythes of the Emperor Chapter during the Damocles Gulf Crusade

The Imperium's response to such sedition was slow in coming, but when it finally arrived, was characteristically brutal. The Tau were condemned as a dangerous xenos species and the Damocles Gulf Crusade was launched to expel them from the region. The Imperial forces were vast, based around a dozen capital ships, and included nineteen regiments of Imperial Guard and five provisional companies of Space Marines made up from a dozen Chapters.

The initial battles were stunning victories for the Imperium, as the power of their fleet and the suddenness of their attacks smashed isolated Tau outposts and eliminated outlying colonies. In a short period of intense conflicts, the Tau were pushed back across the Damocles Gulf, although in the later stages of this drive, the Imperium's victories were not so easily won. The planets from which the Tau were driven were subjected to harsh recriminations -- the Inquisition descended upon the remaining human populations and meted out cruel punishments to those who had rejected the Emperor's tenets. Meanwhile, the Crusade followed the retreating Tau across the Damocles Gulf, entering the territory of the Tau Empire itself.

Dal'yth Defiant

The first sign of the invasion came from the scanners of Pra'yen, the outermost planet of Dal'yth Sept. After picking up unusual readings, the Tau switched to long-ranged optics and were shocked to see great rents opening in space, with the massive Imperial Battleships and their supporting fleet emerging out of nowhere. Although the Tau fleet and Pra'yen's well-armed orbital station took a toll upon the Imperial Navy, the way was soon cleared for the Crusade to advance towards Dal'yth Prime. In the largest conflict of the war, Imperial forces landed upon Dal'yth Prime. In this case, they were not taking on a recently converted Imperial world or newly founded colony, but instead were treading upon a heavily populated Tau Sept world. The Imperial drop was contested by swarms of atmospheric fighters, but was eventually successful in establishing a beachhead. Soon, the Imperium's ground forces, with Titans and armoured formations as a spearhead, ploughed relentlessly towards the conurbation of Gel'bryn.

The Imperial advance was stalled by storms of missiles raining down from beyond the hills. When units were detached to drive back the Tau spotters, they were instead engaged by jump troops protected by cloaking fields. Each time Imperial forces attempted to regain momentum they were met by the timely counter-attacks of the Fire Caste. Night was the worst, as under the cover of darkness Tau in advanced Battlesuits made swift, hard-hitting strikes. With the Tau's superior optics technology major losses were inflicted upon the Imperial armour while suffering little damage in return. Mankind's elite Space Marines attempted to land behind Tau lines and regain the initiative, but they were defeated by teams of heavy Battlesuits whose formidable firepower quickly downed their transports.

Despite their losses the Imperial forces continued their advance, and many sectors of Dal'yth were destroyed or evacuated in the fierce fighting. However, with more Tau reinforcements arriving at the front and the Imperial fleet's ability to hold orbit becoming tenuous, the Imperium's momentum was spent. Once the first news of the invasion of the Tyranid Hive Fleet Behemoth reached the ears of the Crusade's commanders, they were finally forced to withdraw, leaving much of their equipment behind. It is conceivable that the Tau could have encircled the Crusaders, but at the Ethereals' insistence the Water Caste opened a dialogue and agreed upon a truce, allowing the invaders an unimpeded retreat.

Preparing For the Storm

After the great battle on Dal'yth, an uneasy peace descended upon both sides of the war-torn Damocles Gulf. Even as many in the Imperium readied themselves for another offensive, more pressing concerns called for a hasty redeployment of Mankind's gathered armies. The Imperium had demonstrated but a fraction of its power, and that had proven enough to hurl the Tau Empire backwards. Yet the Tau had also learned from the engagements, the Fire Caste gaining invaluable insight into Mankind's methods. They had fought a foe that was willing to absorb huge losses, like the Orks, but unlike the Greenskins the Imperial forces used a wider range of tactics and employed a much more impressive arsenal. In the aftermath, the Ethereals demanded a full study of human captives and recovered Imperial equipment.

The Earth Caste declared much of the technology to be inferior, and some was simply too unstable to contemplate using, such as Imperial plasma devices. There were some eye-opening discoveries however, and the Earth Caste was in absolute wonder over a Warp engine they obtained. With no knowledge or understanding of the realm known as the Warp, they found the strange apparatus utterly unfathomable. To their further frustration, the captured humans that had operated it seemed to possess no actual understanding of its mechanisms either, running the equipment solely through the application of superstitious rituals and ear-splitting chanting.

The Advance Continues

In the wake of their war with the Imperium, Aun'Va stood up in the High Council of Ethereals and voiced his concerns. He implored the Ethereal Supreme, Aun'Wei, then in the twilight of his days, for the rights to reclaim Tau losses. The Tau harbour an unquenchable confidence in their own destiny and are determined that their methods are the best. However, after their long retreat across the Damocles Gulf, and their firsthand experience with the formidable forces of the Imperium, many of the Tau were filled with self-doubt. This was not a race that had tasted defeat before, in any of their prolonged endeavours. Aun'Va argued that without action, cracks would form in the foundation of their carefully orchestrated beliefs -- and this must not come to pass. Sensing the truth of this, the ancient Ethereal nodded, leaving the details for Aun'Va to organise.

Aun'Va knew that those worlds disenfranchised by the Imperium could be manipulated, and from communications intercepts, he knew that the sectors around the Damocles Gulf could expect no further reinforcements. Therefore, Aun'Va ordered the Fire Caste to again cross that shifting barrier in space, the burgeoning Tau Empire stretching again into Mankind's realm, this time to reclaim their recently lost colonies. Although he had some reservations about his choice, Aun'Va elected O'Shovah to head the military aspects of the reclamation effort. A protege of the legendary Commander Puretide, O'Shovah was a dynamic and strong-willed leader who had risen to fame during recent campaigns against the Orks. The young Commander's tactical brilliance had already earned him the name of Commander "Farsight" -- for he was able to anticipate and exploit an enemy's course of action as if he already knew the foe's full battle plan. Initially, Aun'Va's choice proved correct -- every planet marked for reconquest was quickly taken. With much of their armed force called away to war on other fronts, the Imperium's remaining defenders stood no chance against the devastating close-ranged strikes and bold thrusts that were Commander Farsight's signature tactics. The whole Tau Empire cheered with news of each of his victories.

A Parting of the Ways

Commander Farsight leading his forces against the Orks

With a single Tau world left to recolonise, Commander Farsight was drawn off-mission by his age-old enemies, the Orks. What started as swift raids to repel the Greenskins the Tau found probing the edges of the newly recaptured space soon turned into a prolonged war against sizable conglomerate of Ork clans who travelled aboard crude asteroid bases known as Roks. In time, O'Shovah's forces cut deeply into the Ork invasion, chasing the ruling Warboss to a nearby "artefact world", a forlorn place long abandoned by the Imperium. Its name was Arthas Moloch, and there, Farsight's forces were engaged by a savage, yet unidentified enemy, while the Orks escaped in the confusion. Little was reported from the battle, save that all the Ethereals that had been accompanying the expedition were slain during the combat and that their mysterious foe had disappeared, leaving Arthas Molach desolate once more. Undaunted by his losses, and despite direct orders to return, Commander Farsight refused to join the other forces of the Tau Empire. Instead, he led the remnants of his army back onto the Orks' trail. They were soon beyond communication range, passing further from home than any Tau had before.

The Tau Empire sent many messages via the chain of communications beacons, accelerator relays on the ends of the system broadcasting their messages deep into the unknown space that the Tau expedition had disappeared into, but no response came back. It was possible that the vastness of space or some strange interference prevented the messages from reaching their recipient, but after many Terran years passed with no reply, it was eventually deemed that the expedition was lost. The Tau Empire mourned the loss of one of their most illustrious Commanders. Years later, however, probes penetrated deep into the region where Commander Farsight had last been seen and beamed back ominous reports: O'Shovah yet lived, and had established his own colonies, known as the Farsight Enclaves, on the far side of the Damocles Gulf. This mysterious betrayal of the Greater Good still haunts the Tau Empire to this day.

Attack from Beyond

Tau Fire Caste warriors of Ke'lshan fight against the menace of the Tyranids of Hive Fleet Gorgon

During the period of consolidation in the wake of the Second Sphere Expansion, outposts alerted the Tau to an encroaching menace. It was Hive Fleet Gorgon that penetrated their realm, and although only a minor splinter fleet compared with some of the larger incursions that had entered the galaxy, the Tau had never faced a threat like that of the Tyranids -- an intergalactic alien menace whose voracious invasions stripped and devoured planets of all living matter. The Tyranids showed a remarkable ability to physically adapt -- evolving between battles to better counter the defenders. Against their onslaught, the Tau were forced to constantly alter their battle plans as new strains of Tyranid creatures morphed to overcome each advantage of tactics, terrain or technology that the Fire Caste employed. The Tyranids annihilated many holdings before grinding to a halt against the Tau's major defensive actions on the contested planet of Sha'draig. Although the planet was ultimately consumed by the Great Devourer, the aliens had been stalled long enough for the Tau to better prepare their defences at Ke'lshan Prime.

In a strange twist of fate, the Sept world of Ke'lshan was first attacked by the forces of the Imperium. A fleet sent to aid in the Damocles Gulf Crusade over a hundred and fifty standard years earlier had only just emerged from the Warp. Faced with a common enemy, the Tau and Imperial leaders agreed to an uneasy truce. The Tyranids could not adapt to two forces acting in concert, and were eventually massacred, ending the threat of Hive Fleet Gorgon. The human armies, too depleted to continue their previously planned assault, were allowed to retreat, bearing Tau honours given to them for their assistance. The Earth Caste of Ke'lshan immediately began to rebuild their battered Sept, the Ethereals telling them to prepare for the eventual return of one, if not both, of their previous invaders.

Second Sphere Expansion Timeline

The Tau have developed their own mode of timekeeping based on the annual cycle of their homeworld of T'au around its star, a unit called a tau'cyr. Except on human planets that are still in the process of being subsumed into the Tau Empire, the Tau do not use the Imperium's dating system. However, for ease of translation, it has been employed here:

  • Second Sphere Expansion Begins (018.M39) - The Ethereal Supreme, Aun'Wei of the Whispered Wisdom, gives the signal to begin the long-planned Second Sphere of Expansion. Aun'Wei's famous speech is well remembered, ending with "the nod that launched a million ships." With new advances in propulsion technology and an already established interstellar empire, the second expansion is marked by more contact with aliens and larger wars.
  • A New Ally (053.M39) - The planet Vespid is absorbed into the D'yanoi Sept. The insectoid Vespid species had long been courted by the Water Caste -- but little was established save for crystal trade agreements. Within days of the Ethereals' involvement, the Vespid Strain leaders convert wholeheartedly to the cause of the Greater Good.
  • N'dras Colonised (383.M39) - Despite Earth Caste reservations from those who want to study inexplicable sensor readings, the planet N'dras is chosen by the Ethereal Council as the prime world of a new Sept.
  • Steady Advancement (576.M39) - Improvements to anti-gravitic motors and new Tau Battlesuit technology (the T-series prototypes) help the Fire Caste complete the annexation of Tash'var Sept.
  • Mistaken Identity (876.M39) - War is declared upon the cruel raiders victimizing the new colonies of Ke'lshan. Believing they have tracked their foes down, the Tau instead destroy the Eldar Maiden World of Lilarsus. Further relationships between the Tau Empire and the Eldar of the Craftworlds continue to be strained.
  • Vior'la Triumphant (600.M40) - A massive Ork fleet invades the Vior'la Sept, but is defeated in a masterful campaign. Vior'la annually passes through a gap between its two stars, a time called the Trial by Fire. This natural event causes deadly plasma storms to ravage the planet, whose inhabitants survive by closing protective domes around their cities. The Ork Warlord Garskrak and his invading army are lured into this deadly plasma storm where they were utterly destroyed by the raging plasma radiation.
  • Mass Migration (896.M40) - The greatest Water Caste envoy, Por'O Dal'yth Kais Twi Lui'tan, better known as the "Golden Ambassador," leads the effort to recruit alien worlds into the Tau Empire. During this period the Thraxians, Greet, and Formosians are welcomed into the fold. The Hrud and Arache reject the proposals and are driven out of the region.
  • A Legend is Born (651.M41) - The birth of Commander Puretide, the pride of the Dal'yth Sept. His brilliant campaigns later conquer half a dozen star systems for the Tau Empire. Under his authority, the Tau envelop those who can be embraced, seize what can be conquered and obliterate those who defy the Greater Good.
  • The Once and Future Master (731.M41) - The elderly Commander Puretide is urged to view the new colonies across the Damocles Gulf before retiring. While inspecting a colony, Puretide is wounded during a raid. Unable to walk again, the most revered of military leaders spends his remaining years atop Mount Kan'ji, on Dal'yth, where he is kept alive for many more decades using advanced Tau biomedical technology. Only those who attain perfect scores at the Fire Caste academies are sent to sit at Puretide's hover-throne and learn his wisdom. Thanks to Earth Caste holographic technology creating interactive copies of  Puretide's teachings, this tradition is still maintained, although few students are deemed worthy of receiving this high honour.
  • The Arkunasha War (733.M41) - The Arkunasha War is a decade-long conflict in which a populous Tau colony is besieged by Orks. It is especially notable for the rise of the brilliant Puretide prtotégé named Commander Farsight.
  • The Damocles Gulf Crusade (742.M41) - The Tau Empire comes under attack by an armada of the Imperium's warships on a crusade to reclaim their long-neglected territory in the Eastern Fringe. It is a bloody campaign, which is finally stymied at Dal'yth Prime. The retreat of Imperial forces marks the end of the Second Sphere Expansion.

Second Sphere Expansion Septs

Sigils of the Second Sphere Tau Septs

The Second Sphere Expansion of the Tau Empire began in 018.M39, under the orders of Ethereal Supreme Aun'Wei of the Whispered Wisdom. With new advances in propulsion technology and an already established stellar empire, the second expansion of the Tau Empire was marked by more contact with aliens and larger wars. Around 742.M41, the Tau Empire came into conflict with the human Imperium of Man, who launched the Damocles Gulf Crusade in order to keep the Tau's expansion into Imperial-controlled space in check. The retreat of Imperial forces after their defeat marked the end of the Second Sphere Expansion. Of note are the Tau Septs founded by the actions of the Fire Caste's Commander Farsight during this period:

  • Au'taal - Au'taal Prime is a verdant and beautiful Sept, where only honoured heroes of the Tau Empire can retire.
  • N'dras - For reasons known only to the Ethereals, this once thriving Sept has largely been abandoned. Its remaining inhabitants are regarded as untrustworthy, quick-tempered, and of a brooding countenance highly unusual for Tau.
  • Ke'lshan - Situated near the Perdus Rift, this Sept has suffered many invasions and is less trusting of aliens than other Tau. The Ke'lshan fleet and Fire Caste forces are only recently back to full strength after their clashes with Hive Fleet Gorgon. Tau from this Sept have grown mistrustful, solemn, taciturn, unfriendly and sometimes openly hostile to alien races as a result of their experiences.
  • Elsy'eir - A densely populated Sept with many moons orbiting its prime world, most of which are mined for the valuable ores used in the construction of Battlesuits. This Sept is known for its poetry and artwork. Its citizens are considered intellectuals and well-respected for their creativeness by other Tau. The Earth Caste is dominant on Elsy'eir.
  • Tash'var - A frontier sept, those of Tash'var have been subjected to frequent Ork invasions and pirate raids. As a result, its people have become tenacious and hardy.
  • Vash'ya - Known as the world "between spheres" the Sept was settled near the end of the Second Sphere Expansion, as it took a long period for the Earth Caste's terraforming machines to make the air breathable. Major Air Caste fleets and many defence platforms are docked around the Sept world.
  • T'olku - T'olku is known for its many large Ethereal temples, as well as the alien institutes, where many alien ambassadors are brought to be instructed in the ways of Tau culture and society before being assimilated back into their respective homeworlds.

See Also


  • Codex: Tau Empire (6th Edition), pp. 13-16, 21, 28-29, 56, 58
  • Farsight Enclaves - A Codex: Tau Empire Supplement (6th Edition)
  • Warhammer 40,000 - Apocalypse War Zone: Damocles, pp. 6, 8