Ive added a qualifier to your edit on helmets in Late Roman army   Despite the apparent cheapness of manufacture of their basic components many surviving examples of Late Roman helmets including the Intercisa type show evidence of expensive decoration in the form of silver or silvergilt sheathingSouthern  Dixon   Bishop  Coulston   A possible explanation is that most of the surviving exemplars belonged to officers and that silver or goldplating or mounted gemstones denoted rank eg the Deurne helmet believed by some historians to have belonged to a senior officerGoldsworthy   Best wishes