Illustrations of Sassanid Persian Clibanarii

[Urselius]

I think that mail-and-plate is inherently less likely than a system of strapping for any putative plate girdle for Roman cataphract use, because we know that the Romans used leather strapping for articulating armour. Julian's description could merely indicate that gaps between plate elements in cataphract armour exposed an underlying mail shirt. This would work for the shoulder and the gap between torso and leg armour, though the hands would have to have been covered by separate mail defences.