Quote Originally Posted by Slim_Ghost
I agree about having to see, but about hearing I beg to differ.

I have read about this in a mag once, where a researcher set up mock battles between legionnaires in fully authentic Roman armor. The noise from the fighting is too loud for the legionnaires to hear the commander. The only possible way to direct order is by using banners (or the totem-like thingy with the eagle on top).

I still think that the helmets are designed to minimize the amount of iron used while at the same time provides the highest protection on the vital areas (the scalp and the back of the neck). The ear is not protected because the damage to the ear won't be fatal, and possibly won't be that much important since you can't hear anything in the midst of battle anyway.
The Romans used horn blasts to direct their soldiers, the very low notes carry over the noise of battle and the flanges on the IG helemets trap the noise and it reverberates inside your skull. Believe me, it works, apparently gives you a bit of a headache after the battle though.