M. Junkelmann, Römische Helme: Sammlung Axel Guttmann, VIII, Mainz, 2000, pp. 138-139, pls. 65-66, XII and back cover (AG 501).
Cf. H. Russell Robinson, The Armour of Imperial Rome, London, 1975, p. 45 ff. for similar helmets of Imperial Gallic type.
Almost certainly belonging to an officer, the above helmet is of polished tinned bronze which was intended to give the impression of silver and had the added advantage of not tarnishing.