Starting an auxillia unit.

[Peroni]

Coolus helms will be too early for us...

Hmmm... Look at this.. from Trajan's Column..

and Itallic G (too late).

This is also from the Column... Very similarly decorated helmets to the
I-I-G (Hebron helmet) Although dated to a Hadrianic context it could easily be an older helmet.



My full article can be seen here.... http://www.romanarmy.net/trajhelmets.htm

Iron helmets of the Imperial Gallic type have been found in soldier's graves such as the Gallic A from Nijmegen (found with a round iron shield boss) The Gallic E from Idria pri Baci and the Gallic D Verdun.

All found with bent swords and round bosses (typically interments and bent swords are a non-Roman practice)