Face mask or face guard in late roman period

[Robert Vermaat]

Something like this?
[attachment=6468]Cornutionparade.jpg[/attachment]

The man in the middel is a wearing a 3rd century Persian helmet with a Persian mail aventail, also an item not proven for Roman cavalry. The man on the right is wearing a version of the English Sutton Hoo helmet, 'similar to' Sassanid and Roman ridge helmets, but dating to the mid-7th century, while this scene is 300 years earlier.

While I like the way the artist has tries to 'translate' Ammianus' passage, it's also clear that no Roman helmet could be used from any of our sources.