I haven't seen this anywhere else and I thought you might be interesed in knowing
it.
All this information can be gotten out of White Dwarf #261.
There are four (sort of five) Tau castes. The ones that bear the Marathon symbol are the Fire Caste. They are the soldiers of the Tau. These infantry carry long carbines that have huge range and good stopping power. The Tau are terrible melee combatants and feel that it is "uncivilized" to fight up close and personal. I'm sure there will be more info once the Tau Codex is published.
