Leather Cuirass Lorica Musculata, I used to think no way but

[FlaviusCrispus]

Just to clarify a point, Constantine's father, Constantius I Chlorus, was not killed fighting the Picts (except in the movie "Constantine and the Cross"!); he apparently died of some kind of illness or overexertion at York after a campaign. There's some evidence he knew he was dying some weeks or months in advance, since he made a special effort to call his son (who was on the staff of Galerius) to his side.

Most Roman emperors and/or generals certainly "led from the rear" of a battle, but there are plenty of stories of Caesar and others finding themselves in the thick of the fighting through some turn of events. So one would expect even the highest officers would wear protective armor while in the field.

There is solid documentary evidence that at least some cuirasses were made from something other than metal: Cassius Dio writes that Caracalla wore a breastplate made of (presumably layered or molded) linen made (painted?) to look like a metal one, because he was too physically weak to bear the weight of the real deal. This confirms a couple of things: (1) There was a class of "faux armor" worn by at least some high officers in some (probably not combat) situations, (2) it was made to resemble "real" armor, which was invariably metal, and (3) you were considered something of a wuss (American term of "lightweight") for wearing it.

Now, does this non-metallic stuff constitute true "armor," or is is really a form of "triumphal military costume"? That's the rub.