In the case of the unit to which I were referring, it's the amount of armor. Compare



who is only armored in the front, with these two units: Hellenic Cataphracts and Grivpanvar, respectively



Grivpanvar ARE usually considered to be the game's best cavalry and cost about 1.7 times as much as the Persians. They have a 5 attack lance, 11-attack sword with .225 lethality, and 36 defence. Hellenic cataphracts are probably the game's worst cataphracts (According to their unit description, I didn't actually compare stats) with a 4-attack lance, 9-attack AP sword with .11 lethality, and 31 defence. Only thirteen morale, though. Kinsmen have the same stats, but they only have 25 defence. So that's the difference in game terms at least.

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