Cornuti - or not?

[Nathan Ross]

could it possibly have been just an artistic classicization?

I'd say the Constantinian frieze is a long way from classicized. Then again, some of the soldiers are wearing those natty little Attic helmets...

The prominence given to these helmet crests suggests they had some significance (there's a soldier on the left of the 'Milvian Bridge' panel also wearing 'feathers' on an Attic helmet, so clearly they were worn by different troop types).

One suggestion might be that Constantine's men wore feather crests on the front of their helmets to identify themselves in battle - when both sides looked the same, and may even have featured detachments of the same units, telling friend from foe would have been important!