Like a campaign mod that can be nice
Also Swordsmen and Cavalry. I have this in mind:
Daggermen -> Swordsmen -> Legionnaries
Horsemen -> Cavalrymen -> Cataphracts
Sword units could be more effective against spear units and - moreover - against bow units, while cavalry could be extremely effective against sword and bow units (expecially bow units), but suffer alot against spearmen.
For Cavalry units one could replace Pigs with Cattle, and a Cattle Ranch could unlock the chance to build an Horse Paddock. Horse Paddock doesn't need an horse source, and it needs Wheat to function. Horse Paddock unlocks simple Cavalrymen Stables.
Finally, siege units:
Stonethrowers -> Catapults -> Trebouchets
Siege units require Limestone and Copper to work, as well as abit of Wood. Can be built on Siege Workshops, of course.