Tanks are units capable of sustaining large ammount of damage. They are used to absorb the attacking force while damage dealing squads (usually ranged units) attack freely. Tanks have little damage but compensate with threat increasing skills to keep hostile squads concentrated on them.
The tanks of the three races:
Regular: Footman
Elite: Custode
Regular: Judge
Elite: Mindblade
Regular: Bloodclaw
Elite: Goretusk