Example:
List of buildings that would be useful:Archery technology unlocks Archery Range.
Horseback Riding technology unlocks Stables.
Bronze Working technology unlocks Bronze Smithy.
Iron Working technology unlocks Black Smithy.
Archery technology and Archery Range building unlocks Archers.
Bronze Working technology and Archery Range building unlocks Toxotai
Iron Working technology and Archery Range building unlocks Sagitarrii
This would allow Archers to first upgrade to the more expensive AND powerful Toxotai, but then the second upgrade would be more in the line of making them cheaper to build (Iron is notable for being /cheaper/, not stronger, than Bronze. It's Steel that's stronger than Bronze.):
Archers: 2A, 1D, 20 Cost
Toxotai: 3A, 2D, 40 Cost
Sagitarii: 3A, 2D, 20 Cost
Bronze Working technology and Bronze Smithy building unlocks Hoplites.
Iron Working technology and Black Smithy building unlocks Legion
(I've no idea why the vanilla Phalanx(Hoplites), has only a single point of attack. Hoplites were notable because they could destroy unformed armies.)
Hoplites: 2A, 2D, 20 Cost
Legion: 4A, 2D, 40 Cost
Warrior Code technology and Bronze Smithy building unlocks Phalanx.
Feudalism technology and Black Smithy building unlocks Pikemen.
Phalanx: 1A, 3D, 30 Cost; Pikemen
Pikemen: 1A, 3D, 20 Cost; Pikemen
Archery Range: Archers, Archer Cavalry?, Chariots?
Bronze Smithy: Bronze Heavy Infantry, Bronze Longspear
Black Smithy: Iron Heavy Infantry, Iron Longspear
Stables: Light Cavalry, Archer Cavalry?, Gun Cavalry?, Chariots?
???(Archery Track?): Archer Cavalry? Chariots?
War College: Heavy Cavalry, Gun Cavalry?
Siege College: Siege/Artillery
There are others for more modern units, but these come off the top of my head.