Just starting- C3rd Roman

[Robert Vermaat]

I wonder, about the ridge and spangenhelms ... if they were already in use with various eastern 'auxiliary' cohorts, and integrated from them. Or introduced directly from the enemy, the Parthians.

I don't think so. The Parthians used helmets similar to some late Sassanian helmet, but (I'm not sure) I don't think they used the ridge helmet. But even if they did, the Romans already knew the spangenhelmet, which was of Danubian origin and long known from eg the sarmatians. These helmets were also of segmented design, and from the 5th century onwards they seem to have won out over the ridge helmet design. Yet this helmet was not in use in the Roman army during the 3rd or 4th century. I therefore think that the Romans copied the Persian helmets for a reason, and only later decided that the (even more simplified) spangenhelm was better.