Illustrations of Sassanid Persian Clibanarii

[Renatus]

Constantius II was credited with improving the existing Clibanarii rider and horse's armour so may have introduced a metallic chest covering that went over the mail that had previously been worn.

Or in substitution for it. Without some evidence, we cannot know and it would, in my opinion, be a speculation too far to try to attribute to him a development for which, if I understand the argument correctly, there is no evidence until several centuries later. Incidentally, can anyone explain to me why it is necessary to wear mail under plate? It seems like belt and braces to me.