Originally posted by Gogf
Wouldn't a cavalry army be a 6.3.4 unit? Why such a bonus, and why the similar bonus for knight armies?
I don't know who did the original testing and discovered the following information, but it is generally accepted as being true and matches how strong armies feel to me:
Each unit in an army, while attacking, gets an attack strength bonus which is the total of the attack strengths of all units in the army, divided by six.
When defending each unit gets a defense bonus calculated the same way but based on the total defense strengths.
When the army's Civ has built Military Tradition, the bonus is increased by changing the divisor to be 4.
So, if you load an army with all units the same type (as I've done in all cases so far in this game) and supposing those units are 6/3/3 (i.e. Cavalry) then:
Attack bonus with:
Neither Pentagon nor Military Tradition: (6+6+6)/6 = +3
Pentagon only: (6+6+6+6)/6 = +4
Military Tradition only: (6+6+6)/4 = +4 (rounded down)
Both Pentagon and Military Tradition: (6+6+6+6)/4 = +6
With Pentagon and Military Tradition, assuming you load 4 units of the same type into each army, the net result is to simply double their attack and defense stats, because the bonus is (4*X)/4 = +X

Which makes a 4-Cavalry army into a 12/6/4 unit.
This sure makes armies powerful! And makes building Pentagon and Military Tradition a high priority if there will be much fighting in a game.