All of the Intercisa helmets feature an eye motif on the front half of the bowl (clearer on some than others), roughly above where the wearer’s actual eyes would sit, pointing directly forwards. It has become something of a trend for re-enactors to paint the eyes on their helmets, perhaps inspired by the relief in the Via Maria catacomb painting (as seen in the image above) which shows the eye motifs standing out prominently from the rest of the helmet due to their being depicted entirely in black rather than simply a black outline. This is of course only one interpretation of why the relief is decorated so and does raise the question of why the original helmet would have been painted if it was covered in a sheet of precious metals; more elaborate helmets in the Berkasovo family have a similarly placed and shaped eye motif decoration, albeit decorated with intricate reposse work and/or with glass stones in the eye “sockets”. It is entirely possible that the Via Maria relief is instead trying to depict this method of decoration, or simply that the artist wanted the eye motifs to stand out and it is mere artistic convention.
The II also features ten sunken “star” shapes (four-pointed crosses) across the surface, while the IV features recessed crescent moon shapes on the sides of the bowls as well as recessed line work around the edges of the bowl. The IV also features a crest which, unlike most other examples of crest attachment methods we can find in the archaeological record (slots in the central ridge by which the user could attach their crest and remove it as they wished), appears to be welded directly to the central spine. The presence of the crest has led to the Intercisa IV being considered something of an “officer’s helmet”, although (a) the prevalence of helmets with a “fin” crest in artwork seems to imply they are something of a commonplace item and (b) more elaborate decoration survives in examples such as Richborough (amongst many others); it seems fair to say instead then that the Intercisa IV is more likely a common trooper’s helmet, especially given the plethora of repousse-decorated helmets available, to say nothing of the bejewelled Berkasovo I and Budapest. This assertation also does not account for the staggering number of Chi-Rho plates found in the archaeological records that attached to the front of these crests, as well as the frequency these helmets are seen in artworks adorning the heads of what appear to be standard soldiers (see the accompanying picture, a 5th Century boxwood relief from the Museum of Byzantine Art, showing rank-and-file soldiers wearing crested helmets).
What we can surmise reliably is that, whether reconstructions are correct about the jigsaw of pieces discovered at Intercisa or not, it is highly likely the helmets will have looked as lavishly-decorated as we have come to expect (and can see in the reconstruction below) - indeed, whilst some suggest the Intercisa family remained undecorated, the Augsburg helmet (link below) demonstrates that helmets of this type were indeed subject to as much repousse work as some of their Berkasovo family cousins.
As for datation, this type of helmet is seen frequently in artwork from at least the 4th century AD, likely suggesting an earlier presence due to finds paucity, and goes on to feature in Roman artwork from the Eastern Empire well into the 6th century AD, giving it a date range of several centuries. Whilst useful for re-enactment, this sadly does not help us pin down the exact date at which the Intercisa helmets were deposited in the ground.
The Intercisa is still the most enduring helmet seen in the late Roman sphere, partially due to its presence on iconography and partially due to the relative ease with which re-enactors can get their hands on one. It makes sense to use the Intercisa as a “mainstream” helmet for the bulk of reconstructions; due to the sheer amount of them found on-site and the apparent common nature of the pattern, the original Intercisa series can be considered a real workhorse piece of equipment for the Late Roman army.
With thanks to Pavel Simak and Francis Hagan of The Barcarii for help tracking down a relevant source, below can be seen a collection of images showing the superb detailing on the Pustelak Brothers' reconstruction of an Intercisa IV.