M. Junkelmann, Römische Helme: Sammlung Axel Guttmann, VIII, Mainz, 2000, pp. 77, 126, foldouts I and II, pls. 95-102 and X (AG 539) including J. Pollini, "Ein mit Inschriften versehener Legionärshelm", on pp. 169-184.
This helmet is one of only three known examples of this type. The other similar helmets are in the Germanisches Nationalmuseum, Nuremburg, and Budapest Museum. They are all characterised by the same basic shape with a domed skull, stepped occiput, and a steeply sloping neck-guard, similar to the Gallic 'H'. It would have been worn by a legionary infantry soldier, which is also confirmed by the appearance on the neck-guard of the names of the centurions, under whom they would have fought. In the above publication Pollini suggests that the last owner of the helmet would have fought in the campaigns of Domitian or Trajan against the Dacians and the Pannonians.
The punched inscriptions of the helmet's owners read: "Lucius Iunius Sabinus [serving in the centuria] of the Centurion Titus Sario [owns this helmet]", "Gaius Iulius Pro... [serving in the centuria] of the Centurion Pollio", "Marcus Antonius and Publius Ripanius Aturianus(?) [both serving in the centuria] of the Centurion Titus Maximus" and "Lucius Iunius [serving in the centuria] of the Centurion Calventus".
The three surviving bronze Gallic 'I' helmets have all appear to have come from areas where the 1st and 2nd Adiutrix legions were posted. These two legions had been raised by Nero from marines based in Ravenna, eventually having their legionary status recognised by Vespasian (69-79 A.D.). The helmet of the same type now in the Germanisches Nationalmuseum, Nuremberg, was found in the Rhine at Mainz, where the 1st Adiutrix legion had been based. The 2nd Adiutrix served in Britain, before both legions were transferred to Pannonia. Bronze cheekpieces of this helmet type have also been found at Caerleon, England, where a detachment of the 2nd Adiutrix had been possibly based.
Cf. H. R. Robinson, The Armour of Imperial Rome, London, 1975, pp. 58-60, pls 136-143 for the type.