I'm going to stick to my proposal of:
Slave - pure econ, very slowly dies when gathering, perhaps has male and female versions with slightly different roles
Citizen - who can muster into militia when called; has aura that boosts slave gathering, aka "Slave Ownership"; who is the primary builder unit
Citizen-Solders - these are your cheap barracks military units that you use to mass for attacks or defense, who also boost slave gathering rates because they are citizens with the "Slave Ownership" aura; who can build military buildings, but do not gather; who are trained as battalions
Champions - trained in battalions from fortress or special buildings; your professional soldiers; can upgrade each battalion individually with cool units to boost their battalion effectiveness or boost nearby citizen soldier battalions; limited training in some way, either hard limit or some sort of soft limit.
Heroes - some, usually fighters like Leonidas or Scipio Africanus, are trained in battalions, while others, like Chanakya for example, are trained as singles; number of auras is reduced and/or rebalanced.