[Jasper]

Originally posted by Saber Cherry:
I don't mean to imply that cost was the only advantage, as there were many examples of light, mobile units slaughtering sluggish armored ones (the Crusades come to mind). But I think it was a huge factor, and that if the cost had been equal (like in Doms II), heavy units would have made up the bulk of historic armies, rather than light units.

I don't see that being so clear cut. For an easy example, take the Mongols. Probably the best pre-gunpowder army, and mostly comprised of Light Cavalry.

Even the Romans, quite fond of heavy infantry, still kept some lighter troops around for tactical flexibility -- even though they could have fielded armies of purely of heavy infantry.

What it really came down to is that a certain amount of light troops will increased the effectiveness of heavy troops.