|align=center|Highest of the Holy

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== Shas - Fire caste ==

Members of the '''Fire Caste''' are the warriors of the [[Tau Empire]], and as such are most often seen on the field of battle. They have been bred to be the tallest, strongest, and most aggressive Tau, and weak strains are quickly weeded out. These traits come from the Fire Caste's origin on the plains of [[T'au]], where they were hunters and warriors. [[Fire Warriors]], as soldiers of the Fire Caste are known, spend their entire lifetimes in battle or preparing for it, constantly honing their tactics and working to improve their skills. Tau from the world of [[Vior'la]] tend to have slightly greater muscle mass than the norm because of the stronger gravity of that planet.{{Fn|6}}

=== Rising through the ranks ===

Provided the warrior survives four years of active duty, he undergoes the first [[Trial by Fire]], which can be anything from mere gladiatorial affairs to trial by constant combat. If the [[Shas'la]] survives his first Trial by Fire, he is promoted to the rank of [[Shas'ui]], or Veteran. For every consecutive four years of service, the Fire Warrior undergoes another Trial. The higher one's rank within the Fire Caste, the more likely one is to become a [[Battlesuit]] pilot. Upon attaining the rank of '''"O"''', a member of the Fire Caste may be allowed to retire from active duty and become an advisor to the Tau military's command structure, the [[Shas'ar'tol]]. Other than death, this is the only way to leave the Tau military.{{Cite This}}

== Fio - Earth Caste ==

This caste provides for the manufacturing, agricultural, industrial, artisans, and engineering needs of the Tau Empire. By far the largest caste in sheer numbers, it is they who erect dwellings, provide food, and produce new technology. Members of the Earth Caste are often described as plain and dour, possessing a rather stoic outlook on life in general. They were originally the first Tau to build cities and practice agriculture. The city of [[Fio'taun]] is an example of this, being the first place where the [[Ethereal]]s appeared.{{Fn|6}}

==Kor - Air Caste==

The Air Caste is charged with holding the Tau Empire together through the [[Kor'vattra]], the Tau Empire's merchant and war-fleet in addition to operating [[Tau Orbital]]s and [[Fortress Station]]s. Formerly functioning as messengers, these days they are the Tau Navy and are sometimes called the "Invisible Caste", for they rarely if ever set foot upon planets. Living in [[Orbital City|Orbital Cities]], Tau of the Air Caste are the tallest and most slender of all Tau, with long, skinny limbs and hollow bones developed due to lives lived mostly in low- and zero-gravity ships and space stations. In the past, before the time of the [[Mont'au]], the Tau that originally became the Air Caste had membranes stretching between their limbs, allowing them to glide on air currents. Tau pilots tend to be superior pilots compared to their human counterparts because they have a better depth perception and higher G-tolerance, but lack battle-experience compared to the best Imperial fighter-pilots.{{Fn|6}}

== Por - Water Caste ==

The Water Caste serve the Tau Empire as traders, merchants, public servants, bureaucrats, administrators, diplomats, and ambassadors. They interact with other races when such affairs are not handled by the Fire Caste, and often act as administrators of Tau worlds in the absence of an [[Ethereal]] governor. Like water, Water Caste bureacrats fluidly move between other Castes and alien races incorporated within the Emperor to make sure the Tau Empire flows smoothly. The Water Caste tend to be tall and slender compared to other Tau, and are known for their great linguistic, diplomatic, and negotiation skills. Members of the Water Caste are often the ones who initiate first contact with new species encountered by the Emperor, skilfully negotiating their union with the Tau.{{Fn|6}}

== Aun - Ethereal/Celestial Caste ==