For a strategy game which evolves through historic eras like civilisation or rise of nations, I thought of different types of units.

I have:

• Melee specialist, strong against all types of other foot units
• Range specialist, strong against foot units at distance
• Cavalry, strong against all foot units except spears
• Spears, decent in melee, very strong against cav
• Artillery, strong against all types, but highly vulnerable

Did I miss anything? I know that logistics units are very important in real warfare, but I'm not sure how to use them in the game.

6 hours ago, Michael Aganier said:

I wanted your feedback on whether I am missing some important periods, units or even types of units.

This seems a backwards approach to designing your unit roster. I don't think you want to spend time and money on assets and game balance work for redundant units that serve only to confuse the player.  Instead, you should start with a small set of units that work well together, introduce advanced newer units that disrupt existing tactics, and then figure out what they could be. For example, what unit can seriously threaten naked cavemen with stone-blade axes? Someone with good ranged attacks: naked cavemen with stone-blade axes and several spears p.c., which should be at the exact same tech level but much more expensive. 

3 hours ago, LorenzoGatti said:

Instead, you should start with a small set of units that work well together, introduce advanced newer units that disrupt existing tactics, and then figure out what they could be.

I plan to limit the set of units that can be unlocked with research. That way, you indeed only play with a small set of units most of the time and the existing tactics are disrupted by new units that you research or that you encounter.

3 hours ago, LorenzoGatti said:

For example, what unit can seriously threaten naked cavemen with stone-blade axes? Someone with good ranged attacks: naked cavemen with stone-blade axes and several spears

This is a good idea. Thank you for the feedback.

Logistics could work as healing units or effect how far your units can travel away from cities. It depends on what scale your game has, whether your commanding individual troops or whole armies. The Civ games are pretty good to look at for unit ideas though.