\"Celtic\" military technology and the Romans

[Dan Howard]

Many modern illustrators also suggest that late era cataphracts may have worn mail shirts beneath scale or lamellar cuirasses.

This is unlikely. We know that they wore both kinds of armour but I can't think of anything to indicate that both were worn at the same time. Even the Byzantines never wore both until very late in the period - about when the Europeans started layering mail with other kinds of armour.