How well armoured was the Roman army?

[jkaler48]

This is a very interesting topic to me, because I admit it is something I have always wondered about. I feel that at times we tend to "over standardize" the past when in reality, things might have been much more variable. I would imagine this is the case with Roman armor. (And also, I think it makes it more interesting; sure, a whole field full of Roman reenactors decked out in lorica segmentata looks cool, but I think it's even cooler seeing all the different personal impressions that guys have of the soldiers' kit, with different armor, helmets, etc, precisely because I think that might be more authentic!)

Anyway, I'm curious what evidence we might have in the ancient sources to back up the idea of perhaps not all soldiers even being armored at any given battle. Obviously it makes sense for troops like archers and slingers and maybe even some "special" auxilia to not be weighed down with heavy armor, but I admit it is a little hard for me to get my head around the idea of a Roman heavy infantryman not having some sort of body armor.

There are frequent mentioned of "Light Armed" troops in ancient sources. I take this to mean on occasion auxillia without armor but it often seems to refer to Legionary troops
perhaps also without armor and armed with javelins and a lighter oval shield (a few memorials depict this)